Comparison of MIDI Sherlock system and pulsed-field gel electrophoresis in characterizing strains of methicillin-resistant Staphylococcus aureus from a recent hospital outbreak.

An outbreak of methicillin-resistant Staphylococcus aureus infections at the University of Utah Health Sciences Center occurred over a 7-month period. While the isolates phenotypically appeared to be similar in gross morphology and have similar Vitek antibiotic susceptibility patterns, two additional methods of strain characterization were evaluated to enhance the epidemiological investigation: pulsed-field gel electrophoresis and gas chromatography with the MIDI Sherlock system. Sherlock uses gas chromatography to qualitatively and quantitatively analyze the cellular fatty acid composition of organisms and creates two-dimensional plots based on principal-component analysis to define groups of closely related organisms. All isolates were also evaluated by digesting their chromosomal DNAs with the low-frequency-cutting enzyme SmaI and separating the restriction fragments by contour-clamped homogeneous electric field gel electrophoresis. Sample preparation for this pulsed-field gel electrophoresis included a novel cell lysis procedure involving achromopeptidase, greatly reducing the turnaround time. Isolates tested were recovered from the following: 45 suspected outbreak patients, 6 hospitalized patients believed to be unrelated to the outbreak, 6 patients from outside the hospital, and one health care practitioner implicated in the outbreak. Of 45 phenotypically similar suspect strains, 43 clustered tightly on the Sherlock two-dimensional plot. All outbreak patient isolates were also identical by pulsed-field gel electrophoresis with the exception of the same two outliers identified by Sherlock. In this epidemiologic investigation, we found an excellent correlation between the Sherlock and pulsed-field gel electrophoresis results for strain characterization of methicillin-resistant S. aureus.

Infection control and bone marrow transplantation.

BACKGROUND: Bone marrow transplantation for the treatment of malignancies is on the increase. Unfortunately, there are no well-validated infection control guidelines for this highly susceptible population. METHODS: Literature was reviewed concerning infection risks and interventions to decrease risks for bone marrow transplant recipients. RESULTS: Definitive information was generally lacking. However, basic "common sense" infection control recommendations for bone marrow transplantation were made in the following areas: air ventilation systems, design issues, environmental services, patient care issues, barrier precautions, nosocomial surveillance, and discharge planning. Recommendations must be tailored to each facility or setting. CONCLUSION: We conclude that validation of many of these recommendations is necessary to provide optimum care for bone marrow transplant recipients.

Nosocomial outbreak of Legionnaires' disease: molecular epidemiology and disease control measures.

Molecular laboratory techniques were used to study the epidemiology of an outbreak of nosocomial Legionnaires' disease. All patient isolates were Legionella pneumophila serogroup 1 and showed identical plasmid profiles and reactions with serogroup-specific monoclonal antibodies. L pneumophila was also cultured from four of five cooling tower water samples; however, the isolate from only one tower was serogroup 1 of the same subtype as patient isolates. Since the cases were temporally clustered and epidemiologically associated with exposure to cooling tower aerosols, the single cooling tower implicated by molecular analysis was the most likely source of the outbreak. Chlorination of cooling tower ponds has eradicated the epidemic strain. Since potable water also harbored the infecting organism and was the probable source for cooling tower contamination, decontamination of the hospital water system was also undertaken. Superchlorination of hot water holding tanks to 17 ppm on a weekly basis has effectively eradicated L pneumophila from the potable water system and appears to be a reasonable, simple, and relatively inexpensive alternative to previously described methods of control.

Non-gonococcal ophthalmitis associated with erythromycin ointment prophylaxis of gonococcal ophthalmia neonatorum.

Substitution of erythromycin ointment for silver nitrate in the prophylaxis of gonococcal ophthalmia neonatorum (GON) was accompanied by eight infections in 749 (1.1%) well-born and 21 infections in 285 (7.4%) intensive care infants during an eight-month period. This was significantly higher than previous rates of ophthalmitis during the use of silver nitrate, 0.3% (5/1877) and 2.1% (19/904) for well and intensive care infants, (P less than 0.01). Multiple bacteria were isolated, polymicrobial infection occurred frequently and the pattern of bacterial isolates did not favor cross-contamination between infants. Observation suggested the frequent unintentional introduction of ungloved fingers into neonatal eyes during attempts to insert erythromycin ointment. Replacement of ophthalmic ointment with a liquid tetracycline preparation resulted in a decrease in non-gonococcal ophthalmitis to rates similar to the baseline period 8/997 (0.8%) for both nurseries. The increased number of infections appear related to the ointment vehicle, difficulty in its application and the mechanical introduction of bacteria. It is inferred that appropriate application of liquid medication also reduced the risk of inadequate prophylaxis.

An evaluation of daily bacteriologic monitoring to identify preventable episodes of catheter-associated urinary tract infection.

We evaluated the efficacy of a daily bacteriologic monitoring program for preventing symptomatic urinary tract infections (UTI) in hospitalized patients with temporary indwelling urethral catheters. We identified 99 instances in which bacteriuria was present at the time of catheter insertion among 1,140 catheterizations. Of those, 62 patients were asymptomatic and 37 patients had fever or symptoms attributable to UTI. Of the 37 symptomatic episodes, only 14 developed symptoms 24 hours or more after the first culture and might be considered potentially preventable. We also identified 76 episodes of acquired bacteriuria among 608 catheterizations that were initially nonbacteriuric in which at least two cultures were available. Of these 76 patients, 51 (67%) remained asymptomatic throughout their period of hospitalization. Of the 25 patients who developed symptomatic infections, only ten were potentially preventable. In all, only 24 symptomatic episodes among 1,140 catheterizations (2%) occurred 24 hours or more after colonization was first detected and might be considered potentially preventable. Our data suggest that routine daily bacteriologic monitoring of urine from all catheterized patients is not an efficient way to decrease the incidence of symptomatic, catheter-associated UTI.