This week’s review article on this topic comes from Dr. Herbert L. DuPont from the University of Texas School of Public Health and Medical School, Baylor St. Luke’s Medical Center, Baylor College of Medicine, and the Kelsey Research Foundation, all in Houston, TX.
In the United States, approximately 179 million cases of acute diarrhea occur each year, amounting to 0.6 bouts per person per year.In one study, the estimated prevalence of diarrhea among adults the month before questioning was 3 to 7%, with the rate dependent on age, and 8% among children 5 years of age or younger.
• What are the most common causes of acute infectious diarrhea in the United States?
Noroviruses, the principal cause of gastroenteritis, are responsible for approximately 50% of outbreaks of diarrhea, 26% of cases of diarrhea in U.S. emergency departments, and 13% of office visits for diarrhea. Noroviruses are particularly common in closed populations such as cruise ships, nursing homes, dormitories, and hospitals. Data from the Centers for Disease Control and Prevention indicate that infections with the following bacterial pathogens were detected in descending order of rates per 100,000 people in the United States in 2012: salmonella, 16.4 cases; campylobacter, 14.3 cases; Shiga toxin-producing Escherichia coli O157-H7 strain, 1.1 cases; vibrio, 0.4 cases; and yersinia, 0.3 cases.
• What low-inoculum infections often cause secondary spread of illness?
Challenge experiments involving volunteers and epidemiologic studies show that infections with shigella, Shiga toxin-producing E. coli, noroviruses, rotaviruses, giardia, and cryptosporidium are easily spread by low inoculums of agents that often cause secondary spread of illness. Shigella and noroviruses, the most communicable pathogens, have a high potential for person-to-person spread, which is related to the low amounts of inoculum required, the environmental stability of the organisms, and the common occurrence in young children who are likely to spread infection. Limited data from volunteer challenge studies suggest an intermediate dose response for most salmonella and campylobacter strains. Secondary spread occasionally occurs with salmonella strains, and the infection rate among infants is high, suggesting transmission at lower amounts of inoculum.
Morning Report Questions
Q: When is it necessary to send a stool sample to identify the pathogen involved?
A: The determination of the precise cause of diarrhea is costly, and in most cases of nonsevere diarrhea it is not necessary. Assessment of a stool sample to determine the cause of illness should be reserved for patients at high risk for definable diarrhea or cases in which identification of the pathogen would be important. Stool samples should be obtained from patients with any of the following conditions: acute diarrhea that is severe or associated with fever (greater than or equal to 38.5 degreesC), severe diarrhea or diarrhea associated with a severe coexisting condition in a hospitalized patient who is receiving antibiotics (with testing only for C. difficile toxins), persistent diarrhea (greater than or equal to 14 days’ duration), profuse cholera-like watery diarrhea, dehydration, and dysentery. In addition, samples should be obtained from elderly or immunocompromised patients with diarrhea and persons employed as food handlers, those confined to a nursing home, and those who work in a day-care center. Identification of the pathogen is also important in an outbreak of diarrhea.
Q: When are antibiotics indicated in the treatment of acute infectious diarrhea?
A: Empirical antibiotic therapy is recommended for sporadic cases of febrile dysentery, especially those associated with toxicity that suggests the possibility of systemic infection, as well as for severe cases of travelers’ diarrhea or hospital-associated or antibiotic-associated diarrhea. Antibiotics are indicated in only a small percentage of patients with an established infectious cause of acute diarrhea; in these patients, antibiotics can shorten the illness, decrease transmission, and prevent complications, including death. In selecting specific therapy for most cases of acute diarrhea, an etiologic diagnosis must be established. Currently, antibiotic therapy is not helpful in cases of mild salmonella diarrhea, and it lengthens shedding for 3 weeks or longer. Some antibiotics induce Shiga toxin-encoding phage and may precipitate the hemolytic-uremic syndrome. Therefore, in an outbreak of bloody diarrhea, antibiotics are not currently recommended for patients with minimal or no fever who have Shiga toxin-producing E. coli infection.
Table 1. Recommendations for the Diagnosis and Treatment of Organism-Specific Enteric Infection in Adults.