Medical progress - Contagious acute gastrointestinal infections

Acute gastrointestinal illness is exceedingly common; viruses, bacteria, and protozoa are the principal recognized causes. Some causative organisms, such as calicivirus, rotavirus, astrovirus, adenovirus types 40 and 41, S. typhi, and shigella, are indigenous to humans; person-to-person spread follows direct contact or human contamination of food or water. In contrast, nontyphoidal salmonella, campylobacter, and pathogenic E. coli are prevalent in meat, poultry, and dairy foods; human-to-human spread is documented infrequently relative to the total number of cases of infection with these bacterial agents. This lower rate of documentation may reflect the difficulty, in an individual case, of determining whether some common food source is responsible or in distinguishing an environmental source from a human source. As a general matter, the failure to identify a common source for most sporadic, presumably viral, acute gastrointestinal illnesses does not exclude the possible link to an unrecognized foodborne outbreak. The essential point remains, however, that -even though the visibility of an outbreak tends to focus attention on foodborne infection-the great majority of cases are sporadic and spread from person to person. Although free-living protozoa, such as cryptosporidia or giardia, are widespread in nature, contagion is also well documented. The likelihood of contagion depends on the age and self-reliance of an infected person, the nature of the social interaction within the potentially involved group, the intensity of the symptoms, the concentration of organisms in the potentially infective material, the likelihood that the organism will survive direct transmission or survive in the environment, and other, less well understood factors. The immune status of the host undoubtedly plays a role in determining whether symptomatic disease or subclinical infection results, but the nature of such immune factors is poorly understood. Within families, young children are the usual source for contagion because of their exposure to other children, their imperfect personal hygiene, and their dependence on adults. Severely affected persons are more contagious because they discharge greater volumes of infective material that contain large numbers of infectious particles. The likelihood of contagion varies with the concentration of organisms in excreta, the capacity of the organisms to survive and replicate in food or persist in the environment, and the number required to infect Spread of acute gastrointestinal illness is common and problematic in all closed environments such as day-care centers, schools, and cruise ships. Person-to-person transmission is best prevented by the practice of excellent personal hygiene both by infected persons and by those exposed to them. Fecal-oral transmission is the usual route of spread of acute gastrointestinal illness, but caliciviruses and probably adenoviruses are present in vomitus, so kissing or sharing utensils should also be avoided. Dilution by handwashing reduces the inoculum of causative organisms, greatly diminishing the risk of contagion. There is no apparent benefit from the antibacterial agents in soaps, although the regular use of alcohol-based gels will probably reduce transmission. The use of diluted household bleach on environmental surfaces may be necessary to interrupt transmission of viral or protozoal agents. Copyright © 2004 Massachusetts Medical Society.