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Home , Salmonellosis, Shigellosis

Editorial

Nosocomial and

Herbert L. DuPont, MD

In this issue of Control and Hospital interest, however, and should stimulate further study Epidemiology, Paton et al1 report the results of a in this institution as well as others. The authors clearly six-month study of the occurrence of and documented the occurrence of nosocomial salmonel- infection determined by routine rectal swab losis. They provided evidence that at this institution, culturing of patients either admitted to a large acute the epidemiology of nosocomial salmonellosis shows and tertiary care hospital in Nairobi, Kenya, or experi- some difference between children and adults. Prior encing a nosocomial episode of acute during use of antimicrobial agents, presence of clinical mark- a six-month period of time at the same institution. The ers of malnutrition, and coming from more crowded background infection rate for 667 sequentially admit- homes were important to the occurrence of noso- ted patients was approximately 3% for both agents. comial salmonellosis in the children. Although values Salmonella infection at the time of admission was seen of significance were not quite reached, Salmonella only in the children under 13 years of age. These infection in adult cases of nosocomial diarrhea infected children were older and were found more appeared to more commonly be associated with sero- commonly to have clinical indication of malnutrition logic evidence of human virus than culture-negative children. Diarrhea was more (HIV) infection than with prior hospitalization in the common as a presenting finding in the culture-proven last month. The major similarity in both children and cases. The high background rate of infection undoubt- adults was that both commonly had preexisting host edly reflected the low socioeconomic level and under- health impairment (malnutrition, crowding, HIV infec- lying health of the population served by this hospital tion, or previous hospitalizations). where evidence of malnutrition and previous admini- In considering the problem of diarrhea occur- stration of antimicrobials in the previous month were rence after hospitalization, it is important to make a seen in 26% and 66% of children, respectively. Salmo- distinction between hospital-associated diarrhea and nella was recovered from 10% of 360 nosocomial nosocomial infectious diarrhea1 disease.2 Diarrhea diarrhea cases, while Shigella infection in these cases occurring in the hospital is either the first or the occurred no more commonly than in the patients second most common nosocomial illness, and it often admitted to the hospital. is not infectious in origin. Changes in body flora, A hospital-based survey of a specific infection , and tube feedings are important causes of over a restricted period of time (in this case, six diarrhea in the hospital. In the case of infectious months) can yield data with only limited application to diarrhea1 disease, there are important causes of diar- other settings. A few findings in the study were of rhea in the hospital. In the case of infectious diarrheal

From the University of Texas Medical School and School of &blic Health, Houston, Texas. Address reprint requests to Herbeti L. DuPont, MD, Medical School and School ofPublic Health, Centerfor Infectious Diseases, 6431 Fannin, 1.729JFB, Houston, TX 77030. DuPont HL. Nosocomial salmonellosis and shigellosis. Infect Control Hosp Epidemiol. 1991;12:707-709.

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disease, there are important differences when com- intestinal flora and the associated organic acids nor- pared with other nosocomial . Nosocomial mally produced by floral fermentation of dietary car- infectious diarrheas typically represent exogenously bohydrates. The facilitation of intestinal colonization acquired infections. Clustering of cases commonly of Salmonella by concomitant administration of antim- occurs, and healthy patients and hospital personnel icrobials compounds the problem of indication for may become infected. Even though the causative therapy of the disease. Asymptomatic Salmonella agents of infectious diarrhea are characteristically intestinal infection and mild cases of disease probably high-grade pathogens, age and debility can predis- should not be treated with antimicrobials, which tend pose to infection as seen in the Nairobi study. The to promote prolonged organism carriage. However, frequency of nosocomial infectious diarrhea1 disease because bacteremia complicates intestinal salmonel- is unknown, because most cases are not documented losis in just under 10% and dissemination occurs in nor worked up for cause. The actual incidence is far newborns and in the immunosuppressed, antimicrobi- greater than evidence would suggest. The mode of als should be given to the more severely ill or more spread characteristically is the fecal/oral route by debilitated patients with Salmonella infection. The cross infection. Patients typically acquire the organ- antimicrobial agents should be given in these cases ism indirectly from another patient via hands of for more than two weeks, and follow-up cultures hospital personnel. Occasional outbreaks occur fol- should be obtained up to 21 days after therapy.‘j lowing exposure to contaminated food, medication, or One of the unexplained observations is the rela- test reagent. tive rarity of nosocomial shigellosis. All humans are Salmonella species, while not the most common susceptible to Shigella in low concentrations, with cause of nosocomial infectious diarrhea, represent healthy adults developing shigellosis following inges- occasional causes in all areas of the world. Between tion of 100 viable organisms.7 While Shigella species 10% and 30% of the reported cases of Salmonella are potentially the most communicable of bacterial infection in the United States occur in institutions pathogens, in the National Nosocomial Infection Study, (hospitals, nursing homes, and custodial institutions). shigellosis was reported in only one of the 3,363 These outbreaks only account for 1% of reported patients diagnosed with nosocomial enteric infection cases, however, because the average institutional identified during 198&1989. The Nairobi study, while outbreak involves six persons, compared with nonin- documenting the presence of Shigella in newly hospi- stitutional outbreaks of salmonellosis involving an talized patients, failed to provide convincing evidence average of 69 persons. It is believed that nosocomial for important nosocomial spread of the organisms. infection is more common in the developing world.3,4 In controlling the spread of enteric pathogens, In previous publications, hospitals in developing attention must be paid to decreasing the chance of regions have been shown to be important reservoirs cross infection. Effective handwashing must be prac- for the transmission of multiresistent Salmonella, ticed by hospital personnel while caring for patients where receipt of prior antimicrobials, young age, and with diarrhea and while working in newborn nurseries debilitation in addition to hospitalization have predis- or with debilitated patients. Infected personnel should posed to infection. 3*4 Fifty percent of nosocomial cases be relieved of patient contact or food preparation/ of salmonellosis reported in the United States occur in serving while infected until fecal cultures become newborn nurseries and pediatric wards. The new- negative. Prompt outbreak investigation should be borns who have a predilection for disease have a high initiated when two or more cases of diarrhea occur, rate of bacteremia, disseminated focal disease such as and during outbreaks, it is advisable to isolate infected meningitis, , , and long-term patients in separate rooms. Enteric precautions carriage of the infection strain. Other hospitalized should be employed in these areas. In nurseries patients at greater risk for salmonellosis are the aged where enteric isolation is not possible, a cohort and debilitated. Patients with malignancy more com- system should be instituted during outbreaks. Infected monly experience bacteremic sahnonellosis than other patients should be discharged from the hospital when groups. feasible. Prior administration of an antimicrobial agent is a well-established predisposing event in the occurrence REFERENCES of intestinal salmonellosis.5 In the study reported in 1. Paton S, Nicolle L, Mwongera M, et al. SalmoneZZa and Shigella at a public teaching hospital in Nairobi. Infect this issue, 91% of the culture-proven cases occurring Control Hosp Epidemiol. 1991;12:71@717. in children had received an in the past 2. DuPont HL, Ribner BS. Infectious gastroenteritis. In: Bennett month, compared with a rate of 23% to 35% for the Jv, Brachman PS, eds. Hospital Infections. 3rd ed. Boston, Mass: Little, Brown, and Co.; in press. other subjects with nosocomial diarrhea. The impor- 3. Riley LW, Ceballos 0, Trabulsi LR, et al. The signifxance of tant effect of the antibiotic appears to be reduction of hospitals as reservoirs for epidemic multiresistant Salmonella

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typhimurium causing infection in urban Brazilian children. / 6. Neil1 MA, Opal SM, Heelan J, et al. Failure of to Infect Dis. 1984;150:236241. eradicate convalescent fecal excretion after acute salmonellosis: 4. Hadfield TL, Monson MH, Wachsmuth IK. An outbreak of experience during an outbreak in health care workers. Ann antibiotic-resistent Salmonella enteritidis in Liberia West Africa. Intern Med. 1991;114:195199. JZnfect Dis. 1985;151:79@794. 7. DuPont HL, Levine MM, Homick RB, Formal SB. Inoculum size 5. Pavia AT, Shipman LD, Wells JG, et al. Epidemiologic evidence that prior antimicrobial exposure decreases resistance to infec- in shigellosis and implications for expected mode of transmis- tion by antimicrobial-sensitive Salmonella. J Infect Dis. sion. JZnfect Dis. 1989;159:11261128. 1990;161:255-260.

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