Anita K. Highsmith

The epidemiology of nosocomial infections caused by Klebsiella pneumoniae.

Klebsiella pneumoniae causes serious epidemic and endemic nosocomial infections. We conducted a literature review to characterize the epidemiology of epidemic K. pneumoniae outbreaks. Eighty percent of the outbreaks (20/25) involved infections of the bloodstream or urinary tract. Person-to-person spread was the most common mode of transmission, and nearly 50% of the outbreaks occurred in neonatal intensive care units. No one serotype predominated, and no association was found between serotype and either the site of infection or antimicrobial susceptibility pattern. We used data reported to the Centers for Disease Control (CDC) by hospitals participating in the National Nosocomial Infections Study (NNIS) to describe the epidemiology of endemic K. pneumoniae infections. In the 8-year period from 1975 through 1982 the nosocomial K. pneumoniae infection rate was 16.7 infections per 10,000 patients discharged. The rate of infection at medical school-affiliated hospitals was significantly greater than at nonaffiliated hospitals; furthermore, the rate of infection at large affiliated hospitals was greater than at small affiliated hospitals. The rate of infection varied by service, with the highest rate found on the medicine service. During the 8-year period, 184 deaths were caused by nosocomial K. pneumoniae infections (184 deaths/16,969 infections, case-fatality ratio 1.1%), with higher ratios in pediatrics (5%) where there was a 12% mortality in children infected with an aminoglycoside-resistant strain.

Contamination of Intravenous Infusion Fluid: Effects of Changing Administration Sets

Daily change of intravenous (i.v.) infusion administration sets has been recommended by the Center for Disease Control since 1973 to reduce the risk of infusion bacteremia. To evaluate this recommendation, we undertook a prospective, randomized, controlled trial that compared the rates of i.v.-associated bacteremia, in-use i.v. fluid contamination, and phlebitis in 300 patients whose administration sets were changed every 24 h with those in 300 patients whose administration sets were changed every 48 h. No i.v.-associated bacteremia occurred. Twelve of 600 infusions (2%) had positive infusion-fluid cultures: five in one group and seven in the other. Both groups had comparable rates of phlebitis. In this study population with low rates of fluid contamination, no benefit accrued from changing the administration sets every 24 h instead of every 48 h. In hospitals with low rates of fluid contamination, the routine changing of i.v. administration sets every 48 h will result in substantial financial savings.

Pseudomonas species contamination of cystic fibrosis patients' home inhalation equipment

A prevalence study was undertaken to determine whether aerosol equipment used at home by patients with cystic fibrosis (CF) could provide a reservoir for Pseudomonas aeruginosa or Pseudomonas cepacia. Home maintenance of this equipment was also evaluated for its relationship to contamination. In nine of 36 patients, Pseudomonas species were isolated from one or more pieces of home equipment. Only patients colonized with P. aeruginosa had contaminated equipment. P. aeruginosa was recovered from equipment used by five patients; no P. cepacia was recovered. Aerosolization masks were the most commonly contaminated pieces of equipment (20%), followed by nebulizers (17%), medication syringes (10%), connective tubing (6%), and saline solution (4%). Nebulizers and syringes were significantly more likely to be contaminated if they had been in use for 1 month or longer; nebulizers and masks were more likely to be contaminated if they were cleaned or were rinsed only with tap water after use. We conclude that equipment may serve as a reservoir to reintroduce or perpetuate colonization of some patients with CF, but that contamination of equipment with P. aeruginosa is not common.

Nosocomial Bacteriuria: A Prospective Study of Case Clustering and Antimicrobial Resistance

To investigate the role of cross-infection in nonepidemic nosocomial bacteriuria in a large, university-affiliated hospital, we identified in adult patients admitted over an 11-week period all cases caused by organisms of the same genus, species, and antimicrobial susceptibility and clustered by date of onset and hospital ward. Further laboratory studies were conducted to verify clustering. Among the 3452 patients studied, 194 cases of nosocomial bacteriuria were identified; 49 appeared clustered by epidemiologic evidence. Additional laboratory tests verified clustering in 30 cases (15.5%). We found that 90% of clustered and 76% of nonclustered cases had had previous urinary catheterization; Pseudomonas aeruginosa, Serratia marcescens, and Citrobacter freundii often caused clustered infection while Escherichia coli predominated in nonclustered cases; and resistance to gentamicin, sulfathiazole, and carbenicillin was significantly greater for pathogens from clustered cases than for nonclustered ones. This increased resistance emphasizes the need to prevent cross-infection, even in the absence of epidemics.

Polymicrobial bacteremia associated with lipid emulsion in a neonatal intensive care unit.

Polymicrobial bacteremia developed in 5 of 20 infants in a neonatal intensive care unit during a 48-hour period; 2 infants died. Klebsiella pneumoniae serotypes 21 and 24 and Enterobacter cloacae were isolated from four infants, and K. pneumoniae serotype 24 and E. cloacae were isolated from the other infant. Case-control studies revealed an association between receipt of lipid emulsion on one day and the sub-sequent development of bacteremia (P = 0.0005). Epidemiologic evidence suggested that extrinsic contamination of the lipid emulsion bottles had occurred when the hands of a nurse became transiently colonized with these organisms while she was caring for an infant colonized with K. pneumoniae and E. cloacae. Repeated entry of the lipid emulsion bottle, which was used as a multidose medication, probably resulted in contamination. No further cases occurred after lipid emulsion administration practices were changed. We recommend that, except in a pharmacy where conditions for unit dose distribution exist, lipid emulsion should not be used as a multiple dose medication because repeated entry of the bottles increases the risk of contamination. Furthermore lipid emulsion from one container should be administered to only one infant.

Klebsiella pneumoniae: Selected Virulence Factors that Contribute to Pathogenicity

Klebsiella pneumoniae infections occur in humans of all ages, however the highest risk groups appear to be infants, the elderly and the immunocompromised. One or more virulence factors may contribute to pathogenicity in humans. In this article we review three factors that may mediate virulence: cell wall receptors, capsular polysaccharide, and endotoxin. First, the presence of cell wall receptors enables K. pneumoniae to attach to the host cell, thereby altering the bacterial surface so that phagocytosis by polymorphonuclear leukocytes and macrophages is impaired and invasion of the non-phagocytic host cell is facilitated. Second, invasion of the host cell is also facilitated by the large polysaccharide capsule surrounding the bacterial cell; in addition this capsule acts as a barrier and protects the bacteria from phagocytosis. Third, K. pneumoniae produces an endotoxin that appears to be independent of factors that determine receptors and capsular characteristics. Marked interspecies differences in endotoxin production may correlate with virulence. Although some or all of these factors may ultimately determine virulence, the interaction of these factors in vivo has made it difficult to assess the relative contribution of any one of these virulence factors. The pathogenic mechanisms of K. pneumoniae that ultimately determine virulence remain unclear and will require further study.

Epidemic gram-negative bacteremia in a neonatal intensive care unit in Guatemala.

BACKGROUND Nosocomial bloodstream infection is an important cause of morbidity and mortality among neonates. From September 1 through December 5, 1990 (epidemic period), gram-negative bacteremia developed in 26 neonates after their admission to the neonatal intensive care unit (NICU) of Hospital General, a 1000-bed public teaching hospital in Guatemala with a 16-bed NICU. Twenty-three of the 26 patients (88%) died. METHODS To determine risk factors for and modes of transmission of gram-negative bacteremia in the NICU, we conducted a cohort study of NICU patients who had at least one blood culture drawn at least 24 hours after admission to the NICU and performed a microbiologic investigation in the NICU. RESULTS The rate of gram-negative bacteremia was significantly higher among patients born at Hospital General, delivered by cesarian section, and exposed to selected intravenous medications and invasive procedures in the NICU during the 3 days before the referent blood culture was obtained. During the epidemic period, the hospitals chlorinated well-water system malfunctioned; chlorine levels were undetectable and tap water samples contained elevated microbial levels, including total and fecal coliform bacteria. Serratia marcescens was identified in 81% of case-patient blood cultures (13/16) available for testing and from 57% of NICU personnel handwashings (4/7). Most S. marcescens blood isolates were serotype O3:H12 (46%) or O14:H12 (31%) and were resistant to ampicillin (100%) and gentamicin (77%), the antimicrobials used routinely in the NICU. CONCLUSIONS We hypothesize that gram-negative bacteremia occurred after invasive procedures were performed on neonates whose skin became colonized through bathing or from hands of NICU personnel.

Pseudomonas fluorescens bacteremia from blood transfusion

In October 1980, two units of blood contaminated with Pseudomonas fluorescens caused septic transfusion reactions in two recipients at a Chicago hospital; one patient died. Both units had been purchased from the same blood center. Investigation at the blood center and at other hospitals it supplied revealed another fatal case of P. fluorescens sepsis that had occurred one year earlier. Despite extensive environmental culturing at the blood center, the source of P. fluorescens was not identified. However, comparison of the interval between collection and administration of contaminated and non-contaminated units indicated that prolonged storage was a risk factor that may have caused clustering of cases in one hospital. Laboratory studies showed that small inocula of P. fluorescens proliferated in refrigerated fresh whole blood and reached 10(6) to 10(7) colony-forming units per milliliter seven days after incubation. These data suggest that prolonged storage of blood may be an important risk factor for the development of transfusion-related sepsis.

Characteristics of Pseudomonas aeruginosa isolated from whirlpools and bathers.

Pseudomonas aeruginosa is the most frequently isolated microorganism from whirlpool water and lesions associated with outbreaks of dermatitis and folliculitis related to whirlpool exposure. Strains were selected from 19 outbreaks of P. aeruginosa infections (1977 to 1983) associated with whirlpool use; they were examined to determine if the strains possessed unique virulence factors or characteristics that might aid in their selection in the environment. P. aeruginosa, 011, was the predominant serotype isolated from whirlpool water as well as from bathers with dermatitis or folliculitis, followed by serotypes 09, 04, and 03. Antimicrobial susceptibility patterns were similar for all strains. Strains of P. aeruginosa from bathers and water demonstrated statistically significant differences in extracellular enzyme production compared with control strains. P. aeruginosa, serotypes 09 and 011, were found to be sensitive to low levels of chlorine. These data suggest that, if adequate levels of free available chlorine are maintained, P. aeruginosa should have little opportunity to persist in whirlpools. A bathers risk of P. aeruginosa dermatitis or folliculitis appears to be affected primarily by three factors: immersion in water colonized by P. aeruginosa, skin hydration with altered skin flora, and toxic reactions to extracellular enzyme or exotoxins produced by P. aeruginosa. Although a single virulence factor was not identified from the results of this study, there are some indications that the enzymes produced by these microorganisms play an important role in the pathogenesis of disease associated with whirlpool use.

Pseudomonas aeruginosa serotype 0:9: New cause of whirlpool-associated dermatitis

In a five-day period, dermatitis developed in nearly one fourth of the guests staying at a large Georgia hotel. Dermatitis was associated with use of the hotels whirlpool (p less than 0.001) and indoor swimming pool (p less than 0.001). Attack rates were highest among persons more frequently exposed to the whirlpool, in persons under 10 years of age, and during periods of heaviest bather load. Pseudomonas aeruginosa was isolated from skin lesions of 13 of 20 patients from whom culture specimens were taken. Ten isolates were serotype 0:9. The whirlpools water grew P. aeruginosa serotype 0:9; however, the whirlpools automatic chlorinator was functioning properly, the pH of the water was 7.2, and the free chlorine level was 0.6 mg/liter. This is the first report of a whirlpool-associated outbreak caused by P. aeruginosa serotype 0:9. Our findings suggest that this strain may not be readily sensitive to recommended chlorine concentrations.