Diagnosis and Management of Foodborne Illnesses

A Primer for Physicians and Other Health Care Professionals

Produced collaboratively by the
American Medical Association
American Nurses Association--American Nurses Foundation
Centers for Disease Control and Prevention
Center for Food Safety and Applied Nutrition, Food and Drug Administration
Food Safety and Inspection Service, US Department of Agriculture

An earlier edition of this Primer, covering different foodborne illnesses, was published in MMWR in 2001 (MMWR 2001;50[No. RR-2]) and also as a separate publication by the American Medical Association, CDC, the Food and Drug Administration, and the U.S. Department of Agriculture. This report updates and supplements the previous edition. It is being reprinted here as a courtesy to the collaborating agencies and the MMWR readers.

Preface

Foodborne illness is a serious public health problem. CDC estimates that each year 76 million people get sick, more than 300,000 are hospitalized, and 5,000 die as a result of foodborne illnesses. Primarily the very young, the elderly, and the immunocompromised are affected. Recent changes in human demographics and food preferences, changes in food production and distribution systems, microbial adaptation, and lack of support for public health resources and infrastructure have led to the emergence of novel as well as traditional foodborne diseases. With increasing travel and trade opportunities, it is not surprising that now there is a greater risk of contracting and spreading a foodborne illness locally, regionally, and even globally.

Physicians and other health care professionals have a critical role in the prevention and control of food-related disease outbreaks. This primer is intended to provide practical and concise information on the diagnosis, treatment, and reporting of foodborne illnesses. It was developed collaboratively by the American Medical Association, the American Nurses Association-American Nurse Foundation, CDC, the Food and Drug Administration's Center for Food Safety and Nutrition, and the United States Department of Agriculture's Food Safety and Inspection Service.

Clinicians are encouraged to review the primer and participate in the attached continuing medical education (CME) program.

Background

This primer is directed to primary care and emergency physicians, who are likely to see the index case of a potential food-related disease outbreak. It is also a teaching tool to update physicians and other health care professionals about foodborne illness and remind them of their important role in recognizing suspicious symptoms, disease clusters, and etiologic agents, and reporting cases of foodborne illness to public health authorities.

Specifically, this guide urges physicians and other health care professionals to

• Recognize the potential for a foodborne etiology in a patient's illness;

• Realize that many but not all cases of foodborne illness have gastrointestinal tract symptoms;
• Obtain stool cultures in appropriate settings, and recognize that testing for some specific pathogens, eg, E. coli O157:H7, Vibrio spp., must be requested;
• Report suspect cases to appropriate public health officials;
• Talk with patients about ways to prevent food-related diseases; and
• Appreciate that any patient with foodborne illness may represent the sentinel case of a more widespread outbreak.

Foodborne illness is considered to be any illness that is related to food ingestion; gastrointestinal tract symptoms are the most common clinical manifestations of foodborne illnesses. This document provides detailed summary tables and charts, references, and resources for health care professionals. Patient scenarios and clinical vignettes are included for self-evaluation and to reinforce information presented in this primer. Also included is a CME component.

This primer is not a clinical guideline or definitive resource for the diagnosis and treatment of foodborne illness. Safe food handling practices and technologies (eg, irradiation, food processing and storage) also are not addressed. More detailed information on these topics is available in the references and resources listed in this document, as well as from medical specialists and medical specialty societies, state and local public health authorities, and federal government agencies.

Litjen (L.J.) Tan, PhD
American Medical Association
515 North State Street
Chicago, Illinois 60610
(312) 464-4147
(312) 464-5841 (fax)
srt@ama-assn.org (e-mail)

The American Medical Association
  http://www.ama-assn.org/go/foodborne 

Centers for Disease Control and Prevention
  http://www.cdc.gov/foodsafety/cme.htm 

Center for Food Safety and Applied Nutrition,
  Food and Drug Administration
   http://www.cfsan.fda.gov 

Food Safety and Inspection Service, US Department
  of Agriculture
   http://www.fsis.usda.gov 

Food-related disease threats are numerous and varied, involving biological and nonbiological agents. Foodborne illnesses can be caused by microorganisms and their toxins, marine organisms and their toxins, fungi and their related toxins, and chemical contaminants. During the last 20 years, some foods that have been linked to outbreaks include milk (Campylobacter); shellfish (noroviruses); unpasteurized apple cider (Escherichia coli O157:H7), raw and undercooked eggs (Salmonella); fish (ciguatera poisoning); raspberries (Cyclospora); strawberries (hepatitis A virus); and ready-to-eat meats (Listeria).

While physicians and other health care professionals have a critical role in surveillance for and prevention of potential disease outbreaks, only a fraction of the people who experience gastrointestinal tract symptoms from foodborne illness seek medical care. In those who do seek care and submit specimens, bacteria are more likely than other pathogens to be identified as causative agents. Bacterial agents most often identified in patients with foodborne illness in the United States are Campylobacter, Salmonella, and Shigella species, with substantial variation occurring by geographic area and season. Testing for viral etiologies of diarrheal disease is rarely done in clinical practice, but viruses are considered the most common cause of foodborne illness.

This section and the accompanying Foodborne Illnesses Tables summarize diagnostic features and laboratory testing for bacterial, viral, parasitic, and noninfectious causes of foodborne illness. For more specific guidance, consult an appropriate medical specialist or medical specialty society, as well as the various resources listed in this primer. Also refer to this section and the accompanying Foodborne Illnesses Tables when working through the various Patient Scenarios and the Clinical Vignettes portion of this primer.

Recognizing Foodborne Illness

Patients with foodborne illnesses typically present with gastrointestional tract symptoms (eg, vomiting, diarrhea, abdominal pain); however, nonspecific symptoms and neurologic symptoms may also occur. Every outbreak begins with an index patient who may not be severely ill. A physician or health care professional who encounters this person may be the only one with the opportunity to make an early and expeditious diagnosis. Thus, the physician or health care professional must have a high degree of suspicion and ask appropriate questions to recognize that an illness may have a foodborne etiology.

Important clues to determining the etiology of a foodborne disease are the

• Incubation period;
• Duration of the resultant illness;
• Predominant clinical symptoms; and
• Population involved in the outbreak.

Additional clues may be derived by asking whether the patient has consumed raw or poorly cooked foods (eg, raw or undercooked eggs, meats, shellfish, fish), unpasteurized milk or juices, home-canned goods, fresh produce, or soft cheeses made from unpasteurized milk. Inquire as to whether any of the patient's family members or close friends have similar symptoms. Inquiries about living on or visiting a farm, pet contact, day care attendance, occupation, foreign travel, travel to coastal areas, camping excursions to mountains or other areas where untreated water is consumed, and attendance at group picnics or similar outings also may provide clues for determining the etiology of the illness.

If a foodborne illness is suspected, submit appropriate specimens for laboratory testing and contact the state or local health department for advice about epidemiologic investigation. For the physician or other health care professional, implication of a specific source in disease transmission is difficult from a single patient encounter. Attempts to identify the source of the outbreak are best left to public health authorities.

Because infectious diarrhea can be contagious and is easily spread, rapid and definitive identification of an etiologic agent may help control a disease outbreak. Early identification of a case of foodborne illness can prevent further exposures. An individual physician who obtains testing can contribute the clue that ultimately leads to identification of the source of an outbreak.

Finally, health care professionals should recognize that while deliberate contamination of food is a rare event, it has been documented in the past. The following events may suggest that intentional contamination has occurred: an unusual agent or pathogen in a common food, a common agent or pathogen affecting an unusually large number of people, or a common agent or pathogen that is uncommonly seen in clinical practice, as might occur with pesticide poisoning.

Diagnosing Foodborne Illnesses

Differential Diagnosis

As shown in Table 1 and the Foodborne Illnesses Tables, a variety of infectious and noninfectious agents should be considered in patients suspected of having a foodborne illness. Establishing a diagnosis can be difficult, however, particularly in patients with persistent or chronic diarrhea, those with severe abdominal pain, and when there is an underlying disease process. The extent of diagnostic evaluation depends on the clinical picture, the differential diagnosis considered, and clinical judgment.

The presentation of a patient with a foodborne illness is often only slightly different from that of a patient who presents with a viral syndrome. In addition, viral syndromes are so common that it is reasonable to assume that a percentage of those diagnosed with a viral syndrome have actually contracted a foodborne illness. Therefore, the viral syndrome must be excluded in order to suspect the foodborne illness and take appropriate public health action. Fever, diarrhea, and abdominal cramps can be present or absent in both cases so they are not very helpful. The absence of myalgias or arthralgias would make a viral syndrome less likely and a foodborne illness (that does not target the neurologic system) more likely. Foodborne illnesses that do target the neurologic system tend to cause paraesthesias, weakness and paralysis that are distinguishable from myalgias or arthralgias (see below). The presence of dysentery (bloody diarrhea) is also more indicative of a foodborne illness, particularly if it is early in the course.

If any of the following signs and symptoms occur in patients, either alone or in combination, laboratory testing may provide important diagnostic clues (particular attention should be given to very young and elderly patients and to immunocompromised patients, all of whom are more vulnerable):

• Bloody diarrhea

• Weight loss
• Diarrhea leading to dehydration
• Fever
• Prolonged diarrhea (3 or more unformed stools per day, persisting several days)
• Neurologic involvement, such as paresthesias, motor weakness, cranial nerve palsies
• Sudden onset of nausea, vomiting, diarrhea
• Severe abdominal pain

In addition to foodborne causes, a differential diagnosis of gastrointestinal tract disease should include underlying medical conditions such as irritable bowel syndrome; inflammatory bowel diseases such as Crohn's disease or ulcerative colitis; malignancy; medication use (including antibiotic-related Clostridium difficile toxin colitis); gastrointestinal tract surgery or radiation; malabsorption syndromes; immune deficiencies; and numerous other structural, functional, and metabolic etiologies. Consideration also should be given to exogenous factors such as the association of the illness with travel, occupation, emotional stress, sexual habits, exposure to other ill persons, recent hospitalization, child care center attendance, and nursing home residence.

The differential diagnosis of patients presenting with neurologic symptoms due to a foodborne illness is also complex. Possible food-related causes to consider include recent ingestion of contaminated seafood, mushroom poisoning, and chemical poisoning. Because the ingestion of certain toxins (eg, botulinum toxin, tetrodotoxin) and chemicals (eg, organophosphates) can be life-threatening, a differential diagnosis must be made quickly with concern for aggressive therapy and life support measures (eg, respiratory support, administration of antitoxin or atropine), and possible hospital admission.

When submitting specimens for microbiologic testing, it is important to realize that clinical microbiology laboratories differ in protocols used for the detection of pathogens. To optimize recovery of an etiologic agent, physicians and other health care professionals should understand routine specimen-collection and testing procedures as well as circumstances and procedures for making special test requests. Some complex tests (eg, toxin testing, serotyping, molecular techniques) may only be available from large commercial or public health laboratories. Contact your microbiology laboratory for more information.

Stool cultures are indicated if the patient is immunocompromised, febrile, has bloody diarrhea, has severe abdominal pain, or if the illness is clinically severe or persistent. Stool cultures are also recommended if many fecal leukocytes are present. This indicates diffuse colonic inflammation and is suggestive of invasive bacterial pathogens such as Shigella, Salmonella, and Campylobacter species and invasive E. coli. In most laboratories, routine stool cultures are limited to screening for Salmonella and Shigella species and Campylobacter jejuni/coli. Cultures for Vibrio and Yersinia species, E. coli O157:H7, and Campylobacter species other than jejuni/coli require additional media or incubation conditions and therefore require advance notification or communication with laboratory and infectious disease personnel.

Stool examination for parasites generally is indicated for patients with suggestive travel histories, who are immunocompromised, who suffer chronic or persistent diarrhea, or when the diarrheal illness is unresponsive to appropriate antimicrobial therapy. Stool examination for parasites is also indicated for gastrointestinal tract illnesses that appear to have a long incubation period. Requests for ova and parasite examination of a stool specimen will often enable identification of Giardia lamblia and Entamoeba histolytica, but a special request may be needed for detection of Cryptosporidium and Cyclospora cayetanensis. Each laboratory may vary in its routine procedures for detecting parasites, so it is important to contact your laboratory.

Blood cultures should be obtained when bacteremia or systemic infection is suspected.

Direct antigen detection tests and molecular biology techniques are available for rapid identification of certain bacterial, viral, and parasitic agents in clinical specimens. In some circumstances, microbiologic and chemical laboratory testing of vomitus or implicated food items also is warranted. For more information on laboratory procedures for the detection of foodborne pathogens, consult an appropriate medical specialist, clinical microbiologist, or state public health laboratory.

Treating Foodborne Illness

Selection of appropriate treatment depends on identification of the responsible pathogen (if possible) and determining if specific therapy is available. Many episodes of acute gastroenteritis are self-limiting and require fluid replacement and supportive care. Oral rehydration is indicated for patients who are mildly to moderately dehydrated; intravenous therapy may be required for more severe dehydration. Routine use of antidiarrheal agents is not recommended because many of these agents have potentially serious adverse effects in infants and young children.

Choice of antimicrobial therapy should be based on

• Clinical signs and symptoms;
• Organism detected in clinical specimens;
• Antimicrobial susceptibility tests; and
• Appropriateness of treating with an antibiotic (some enteric bacterial infections are best not treated).

Knowledge of the infectious agent and its antimicrobial susceptibility pattern allows the physician to initiate, change, or discontinue antimicrobial therapy. Such information also can support public health surveillance of infectious disease and antimicrobial resistance trends in the community. Antimicrobial resistance has increased for some enteric pathogens, which dictates judicious use of this therapy.

Suspected cases of botulism are treated with botulinum antitoxin. Equine botulinum antitoxin for types A, B, and E can prevent the progression of neurologic dysfunction if administered early in the course of illness. Physicians and other health care professionals should notify their local and state health departments regarding suspected cases of botulism. CDC maintains a 24-hour consultation service to assist health care professionals with the diagnosis and management of this rare disease.

Surveillance and Reporting of Foodborne Illness

Reporting of foodborne illnesses in the United States began more than 50 years ago when state health officers, concerned about the high morbidity and mortality caused by typhoid fever and infantile diarrhea, recommended that cases of "enteric fever" be investigated and reported. The intent of investigating and reporting these cases was to obtain information about the role of food, milk, and water in outbreaks of gastrointestinal tract illness as the basis for public health actions. These early reporting efforts led to the enactment of important public health measures (eg, the Pasteurized Milk Ordinance) that profoundly decreased the incidence of foodborne illnesses.

Often health care professionals may suspect foodborne illness either because of the organism involved or because of other available information, such as several ill patients who have eaten the same food. Health care professionals can serve as the eyes and ears for the health department by providing such information to local or state public health authorities. Foodborne disease reporting is not only important for disease prevention and control, but more accurate assessments of the burden of foodborne illness in the community occur when physicians and other health care professionals report foodborne illnesses to the local and state health department. In addition, reporting of cases of foodborne illness by practicing physicians to the local health department may help the health officer identify a foodborne disease outbreak in the community. This may lead to early identification and removal of contaminated products from the commercial market. If a restaurant or other food service establishment is identified as the source of the outbreak, health officers will work to correct inadequate food preparation practices, if necessary. If the home is the likely source of the contamination, health officers can institute public education about proper food handling practices. Occasionally, reporting may lead to the identification of a previously unrecognized agent of foodborne illness. Reporting also may lead to identification and appropriate management of human carriers of known foodborne pathogens, especially those with high-risk occupations for disease transmission such as foodworkers.

Table 2 lists current reporting requirements for foodborne diseases and conditions in the United States. National reporting requirements are determined collaboratively by the Council of State and Territorial Epidemiologists and CDC. Additional reporting requirements may also be mandated by state and territorial laws and regulations. Details on specific state reporting requirements are available from state health departments and from the Council of State and Territorial Epidemiologists and CDC.

Typically, the appropriate procedure for health care professionals to follow in reporting foodborne illnesses is to contact the local or state health department whenever they identify a specific notifiable foodborne disease. However, it is often unclear if a patient has a foodborne illness prior to diagnostic tests, so health care professionals should also report potential foodborne illnesses, such as when 2 or more patients present with a similar illness that may have resulted from the ingestion of a common food. Local health departments then report the illnesses to the state health departments and determine if further investigation is warranted.

Each state health department reports foodborne illnesses to CDC. CDC compiles these data nationally and disseminates information via the weekly Morbidity and Mortality Weekly Report and annual summary reports. CDC assists state and local public health authorities with epidemiologic investigations and the design of interventions to prevent and control food-related outbreaks. CDC also coordinates a national network of public health laboratories, called PulseNet, which performs "molecular fingerprinting" of bacteria (by pulsed-field gel electrophoresis) to support epidemiologic investigations.

Thus, in addition to reporting cases of potential foodborne illnesses, it is important for physicians to report noticeable increases in unusual illnesses, symptom complexes, or disease patterns (even without definitive diagnosis) to public health authorities. Prompt reporting of unusual patterns of diarrheal/gastrointestinal tract illness, for example, can allow public health officials to initiate an epidemiologic investigation earlier than would be possible if the report awaited definitive etiologic diagnosis.

Finally, new information on food safety is constantly emerging. Recommendations and precautions for people at high risk are updated whenever new data about preventing foodborne illness become available. Physicians and other health care professionals need to be aware of and follow the most current information on food safety.

Patient Scenarios

The learning scenarios in this section can be used to reinforce medical management information pertaining to foodborne illnesses, such as that provided from the previous sections of this primer. The case studies provide questions that need to be considered when dealing with a potential case of foodborne illness. Answers are provided immediately following the questions to enhance the learning process.

Similar learning scenarios are also available for other foodborne pathogens.

Congenital Toxoplasmosis, A Patient Scenario

Susan, a 6-month-old infant, is brought to your office for evaluation of apparent blindness. Her mother reports that she had been well during the pregnancy and the delivery was uncomplicated. The baby appeared healthy until age 4 months, when the parents became concerned about her vision.

Physical examination was normal except for bilateral macular scars, microphthalmos, and unresponsiveness to visual stimuli. There were no other neurologic abnormalities, and her growth and development were appropriate for her age. A computed tomography (CT) scan of the head was obtained.

The CT scan of the child's head showed periventricular calcifications and asymmetric dilation of the lateral ventricles. The mother is 35 years old and reiterated that she does not recall being ill during the pregnancy; however, she also indicated that she would not necessarily remember every little symptom. She also denied having a history of STDs. She had received the mumps-measles-rubella (MMR) vaccine as a child but no vaccines during pregnancy. The mother recalled eating insufficiently cooked meat while traveling in France during the first trimester of pregnancy. The family does not own a cat, and she does not recall having been exposed to cats during her pregnancy.

Results of serologic testing detected both IgG and IgM antibodies to Toxoplasma gondii in both the baby's and mother's serum. The mother's IgM titer was 1:6400 and IgG titer was 1:6400, while those of the baby were IgM titer of 1:160 and IgG titer of 1:6400.

The baby was diagnosed with congenital toxoplasmosis.

Human infection with the intracellular protozoan parasite Toxoplasma gondii occurs globally. Infection is usually subclinical or produces a mild illness, except in immunodeficient persons and fetuses infected in utero. Most infants with congenital toxoplasmosis appear healthy at birth but have a high incidence of developing serious ophthalmologic and neurologic sequelae during the next 20 years of life. Severe congenital toxoplasmosis may be apparent at birth or become apparent during the first 6 months of life. Chorioretinitis, intracerebral calcifications, and hydrocephalus, as in the present case, are typical features

The child was treated with pyrimethamine, sulfadiazine, and folinic acid for 6 months. She remains blind, and has developed moderate psychomotor retardation.

Infection acquired by healthy persons is usually asymptomatic or may lead to painless lymphadenopathy or a mononucleosis syndrome. Maternal infection is usually unrecognized.

Disease in persons with depressed cellular immunity (eg, persons with AIDS, transplant recipients, persons receiving immunosuppressants) usually is due to reactivation of latent infection but can result from acute infection. Toxoplasmosis in these persons leads to lethal meningoencephalitis, focal lesions of the CNS, and less commonly, myocarditis or pneumonitis. The clinical picture may include headache, seizures, mental status changes, focal neurologic signs, and aseptic meningitis. Thirty to forty percent of AIDS patients with IgG antibodies to T. gondii (indicating chronic latent infection) develop active toxoplasmosis unless they take preventive medication.

Congenital infection occurs when a previously uninfected mother develops infection during pregnancy. Infection prior to conception, demonstrated by specific IgG antibodies, in nearly all cases guarantees against infection of the fetus. However, transplacental transmission occurs from mothers whose prior infections reactivate when they receive immunosuppressant medications or develop AIDS. Congenital toxoplasmosis may result in abortion, stillbirth, mental retardation, and retinal damage. Recurrent toxoplasmic chorioretinitis in children and young adults is frequently the result of congenital infection that was asymptomatic at birth.

Acute Hepatitis A: A Patient Scenario

While working in an emergency room, you are asked to see a 31-year-old Asian-American woman who has had fever, nausea, and fatigue for the past 24 hours. She also reports dark urine and has had 3 light colored stools since yesterday. She has previously been healthy and has no previous history of jaundice. Her physical examination shows a low-grade fever of 100.6°F/38.1°C, faint scleral icterus, and hepatomegaly. Her blood pressure and neurologic exam are normal and there is no rash. Initial laboratory studies show an alanine aminotransferase (ALT) result of 877 IU/L, aspartate amino transferase (AST) enzyme levels of 650 IU/L, an alkaline phosphatase of 58 IU/L and a total bilirubin of 3.4 mg/dL. White blood cell count is 4.6, with a normal differential; electrolytes are normal; the blood urea nitrogen level is 18 mg/dL; and serum creatinine level is 0.6 mg/dL. Pregnancy test is negative.
 

She has no children, and her boyfriend is not ill. She has been in a monogamous relationship with her boyfriend for 2 years. She was born in the United States; her parents immigrated to the United States from Taiwan in the 1950s. She works as a food preparer for a catering business. She returned 4 weeks ago from a 1-week vacation in Mexico (Mexico City and nearby areas), where she stayed with her boyfriend in several hotels. She drank only bottled water but ate both cooked and uncooked food at numerous restaurants while in Mexico, and she visited a family friend and her 3 young children in a Mexico City suburb.

She did not receive hepatitis A vaccine or immune globulin before going on vacation. She is not sure if she has received hepatitis B vaccine. She has not gone camping or hiking and had no recent tick exposures. She has never used illicit drugs, drinks alcohol rarely, and has never received a transfusion. She is taking oral contraceptives but no other prescription medication, and took 500 milligrams of Tylenol^® once after onset of her current symptoms. She has a pet cat but no other animal exposures. She had chickenpox and mononucleosis during childhood.

• Total anti-HAV: positive

• IgM anti-HAV: positive
• Total anti-HBc: positive
• IgM anti-hepatitis B core antigen: negative
• HBsAg: negative
• anti-HBs: positive
• anti-HCV: negative

The incubation period for hepatitis A is 15--50 days, with an average of 28 days. The most common signs and symptoms associated with acute hepatitis A include jaundice, fever, malaise, anorexia, and abdominal discomfort. The illness can be severe and approximately 10% to 20% of reported cases require hospitalization. The likelihood of having symptoms with HAV infection is related to the person's age. In children <6 years of age, most (70%) infection is asymptomatic; if illness does occur it is not usually accompanied by jaundice. Older children and adults are more likely to have symptomatic disease, although jaundice may be absent in as many as one third of adults with HAV infection. In many developing countries in Asia, Africa, and Central and South America, infection is nearly universal during early childhood and is often asymptomatic.

Hepatitis A is the most common vaccine-preventable disease among travelers. The risk varies according to region visited and the length of stay, and is increased even among travelers who report observing measures to protect themselves against enteric infection or stay only in urban areas. In the United States, children account for approximately one third of reported travel-related cases.

Prompt reporting of hepatitis A cases allows time to decide on a course of action and provide timely immunoprophylaxis when appropriate. Because this patient works as a food preparer, the health department will need to visit the establishment to assess the likelihood that her duties and hygiene practices pose a significant risk of food contamination. IG is often recommended for co-workers of commercial food handlers with hepatitis A. In addition, if she worked at any time during the 2 weeks before onset of jaundice to 1 week after onset, persons who ate food prepared or handled by this patient may be candidates for IG prophylaxis. Determinations of the need for IG prophylaxis are made on a case-by-case basis by experienced health department personnel. Again, immediate reporting of hepatitis A cases allows time to decide on a course of action and provide timely treatment and intervention when appropriate.

Norovirus Infection: A Patient Scenario

Nancy is a 25-year-old previously well graduate student who presents to the emergency department with a 12-hour history of nausea, diarrhea, abdominal cramping, and vomiting (about 6 episodes), malaise, and a low-grade fever. She describes her onset of symptoms as sudden.

Physical examination shows that Nancy is afebrile with a supine blood pressure of 123/74 mm Hg. She has a diffusely tender abdomen and is dehydrated. Stool examination is negative for occult blood.

Nancy reports that she rarely has diarrhea or vomiting. She also reports no contact with anyone who was ill in the past week, nor has she been out of the country in the past month. Her boyfriend, who does not live with her, has similar symptoms with an almost identical onset time. Both attended a wedding 2 days ago. The meal at the wedding reception, which was held at a local reception hall, was the only meal they shared in the past several days. Nancy does not know if anyone else who attended the wedding became ill. Nancy reports that she has no history of a sexually transmitted disease and that she and her boyfriend have a monogamous sexual relationship.

At the wedding, the couple had a choice of meal. Nancy had lobster tail and filet mignon. Her boyfriend had chicken. They both consumed stuffed mushrooms, salad, and hors d'oeuvres preceding the main meal. For dessert they both had wedding cake and fresh fruit. Both drank wine or beer during the reception.

The couple attended a barbecue the previous week. This outing was a function sponsored by Nancy's employer. Nancy tells you that none of her co-workers have been ill with vomiting and diarrhea.

You place an inquiry with the local health department about the possible outbreak. The health department notifies you that an investigation is currently under way. Illness has also been reported among 75% of attendees at a wedding the day before the one Nancy attended, at the same reception hall. The only common food between the 2 weddings is the salad, and the health department currently suspects a food handler who worked during both weddings who was experiencing diarrhea. Most patients have reported nausea, vomiting (about 90%), and diarrhea (70%), with some fever, malaise, headache, chills, and abdominal pain. The mean incubation period for those who have reported illness is 28.6 hours, with a mean duration of 31.8 hours.

The health department suspects viral gastroenteritis caused by a norovirus. A norovirus is suspected because of the rapid onset of symptoms, the short 36-hour incubation period and relatively short duration of illness, the absence of bloody diarrhea, and the high percentage of vomiting. Bacterial cultures are negative for enteric pathogens on stool samples collected thus far.

The health department requests that a stool sample be collected. The sample should be collected in a sterile container without transport media, and kept at 4°C (40°F) until shipped. The sample should be shipped on ice packs to the local health department laboratory for testing. The health department also asks you to encourage Nancy's boyfriend to submit a stool sample.

Proper hand washing procedures can prevent the spread of the virus between persons. Hands should be washed under warm water with soap for approximately 15 seconds to prevent fecal-oral transmission.

Antibiotic-Resistant Salmonellosis: A Patient Scenario

Andrea brings her 3-year-old son, Marcus, to your office with a 2-day history of low-grade fever, nausea, and 6--8 watery stools per day. Marcus has also been complaining of abdominal pain and feeling tired. He has been eating and drinking less than usual. His medical history is remarkable for recurrent otitis media, for which he was prescribed oral antibiotics 10 days prior to this visit.

Physical examination reveals a well-developed boy who appears fatigued. Vital signs are remarkable for low-grade fever (99.5°F/37.5°C). He does not have signs of dehydration. His otitis appears resolved and he has a normal cardiopulmonary exam. The abdominal exam reveals hyperactive bowel sounds, mild diffuse tenderness, and stool negative for occult blood.

Marcus has not had similar episodes of diarrhea in the past. He attends preschool and is cared for by his grandmother after school in her home. He last visited a petting farm 3 months prior to this illness. Their family returned the previous day from a 5-day Caribbean cruise. Marcus was diagnosed with otitis media 4 days prior to their departure and was prescribed a 1-week course of oral antibiotics. Andrea has had nausea and 3--4 loose stools per day for the previous 2 days. She has not had any fever, abdominal pain, or vomiting. Marcus' father and two sisters also traveled on the cruise and are asymptomatic. None of the family members took prophylactic antibiotics for travelers' diarrhea during the cruise.

The additional history suggests that Marcus' and Andrea's illness may be an infectious gastroenteritis related to their recent travel. Antibiotic-associated colitis caused by Clostridium difficile infection must be considered since the child was prescribed antibiotics for otitis 8 days prior to this illness. Given the recent onset, travel history, and his mother's symptoms, it is unlikely that appendicitis, celiac disease, or inflammatory bowel disease are the etiologies of Marcus' illness.

The most likely diagnosis is infectious gastroenteritis.

An open-ended food history reveals multiple common meals eaten by Andrea and Marcus. Andrea denies the consumption of unpasteurized milk, raw shellfish, and undercooked meats. She does report that, unlike the rest of the family, she and Marcus used to wake up early enough to enjoy the breakfasts served on board the cruise. Breakfast served on the cruise consisted of a choice of French toast or pancakes with fruit compote, scrambled eggs or omelets made to order, potatoes, and fresh fruit along with a choice of beverages, including milk, coffee, and tea. Andrea complained that the eggs were occasionally runny. Several fellow passengers told Andrea at breakfast that they were experiencing vomiting and diarrhea. Andrea and Marcus ate the remainder of their meals with the entire family. They did not drink any untreated water or eat items purchased from street vendors at ports of call. In response to your other questions, Marcus does not have a reptile at home. Andrea has not been prescribed antibiotics for more than 1 year. The family lives in a city and has access to municipal water.

Based on the additional historical details, it appears that many people on board the cruise were experiencing symptoms of vomiting and diarrhea. This suggests an outbreak of infectious gastroenteritis that may be related to a common food or water source on the ship. The etiologic agent may be bacterial, viral, or parasitic. The most likely bacterial organisms causing this diarrheal illness are Campylobacter jejuni, Escherichia coli, Shigella species, and Salmonella. C. jejuni is the most common bacterial cause of diarrheal illness in the United States. Outbreaks of C. jejuni have been linked to raw milk, poultry, eggs, and water. Enterotoxigenic E. coli (ETEC) is recognized as the most common cause of "travelers' diarrhea" and can be transmitted via food or water. Salmonella is an important bacterial cause of foodborne illness, ranking just behind C. jejuni in its frequency. Vehicles most commonly implicated in foodborne outbreaks of salmonellosis include beef, poultry, produce, eggs, pork, and dairy products. Large waterborne outbreaks of salmonellosis have occurred rarely.

Three days after the initial visit, Andrea feels better with fewer stools per day, but Marcus has had worsening vomiting and diarrhea. He has had several episodes of high fever and has not been drinking ORS adequately. In the office, Marcus is febrile (102°F/38.8°C) and appears dehydrated with dry mucous membranes and decreased skin turgor. No significant change is noted in the abdominal examination. You admit Marcus for intravenous hydration and encouragement of oral rehydration and consider a change in antibiotic therapy. Because of the progressive systemic nature of his illness, you also obtain blood cultures at this time.