Evaluation of the quantitative antibiogram as an epidemiological tool for the prospective typing of methicillin-resistant Staphylococcus aureus (MRSA), and comparison with ribotyping.

The method is based on the multivariate analysis of inhibition zone diameters of antibiotics in disk diffusion tests. Five antibiotics were used (erythromycin, clindamycin, cotrimoxazole, gentamicin, and ciprofloxacin). Ribotyping was performed using seven restriction enzymes (EcoRV, HindIII, KpnI, PstI, EcoRI, SfuI, and BamHI).

1,000-bed tertiary university medical center.

During a 1-year period, 31 patients were found to be infected or colonized with MRSA. Cluster analysis of antibiogram data showed nine distinct antibiotypes. Four antibiotypes were isolated from multiple patients (2, 4, 7, and 13, respectively). Five additional antibiotypes were isolated from the remaining five patients. When analyzed with respect to the epidemiological data, the method was found to be equivalent to ribotyping.

Among 206 staff members who were screened, six were carriers of MRSA. Both typing methods identified concordant of MRSA types in staff members and in the patients under their care.

The quantitative antibiogram was found to be equivalent to ribotyping as an epidemiological tool for typing of MRSA in our setting. Thus, this simple, rapid, and readily available method appears to be suitable for the prospective surveillance and control of MRSA for hospitals that do not have molecular typing facilities and in which MRSA isolates are not uniformly resistant or susceptible to the antibiotics tested.

To identify characteristics associated with methicillin-resistant Staphylococcus aureus (MRSA) colonization and infection, and to evaluate the efficacy of systemic and topical antimicrobials in the eradication of MRSA carriage among hospitalized patients.

A case-control study was done to identify associations. Odds ratios were estimated by unconditional multiple logistic regression. Cohort study was done to evaluate MRSA decolonization efficacy by an oral regimen. Patients infected or colonized with MRSA received a 5-day course of oral (166 mg/800 mg) trimethoprim-sulfametroxazole twice daily and 600 mg of rifampin once daily as decolonization treatment. The proportion of MRSA-free patients after decolonization treatment was determined. Persistence of clearing was estimated by the Kaplan-Meier method.

Ramón y Cajal Hospital, a 1,249-bed, tertiary-care teaching hospital in Madrid, Spain.

One hundred ninety-two patients with hospital-acquired MRSA infection/colonization and 195 MRSA-free random controls.

Six factors were associated independently with MRSA infection/colonization: age (every 10 years of age, odds ratio [OR]=1.3); ward (surgical, OR=1; medical, OR=3.1; intensive care unit, OR=60); previous hospitalization (OR=6.9); coma (OR=25.3); invasive procedures (each, OR=1.7); 3 or more weeks of hospitalization (OR=3.8). We failed to show antibiotic therapy to be an independent risk factor for MRSA hospital infection/colonization. Overall, MRSA eradication was 64.2% by day 2 to 9 after completion of treatment. Kaplan-Meier product limit survival analysis showed that the probability of remaining MRSA-free was 65.3% (SE=0.09) at 32 days after completion of treatment.

The results offer a rationale for reduction of MRSA infection/colonization in the hospital by interventions aimed at early identification of patients at higher risk, at prompt discharge of patients, and at preventing dissemination while performing invasive procedures. They also provide estimates of antibiotic treatment efficacy to reduce the reservoir of MRSA in the hospital.

To examine the practices toward infection control training and to assess the attitudes about, and risks for, exposures to blood among hemophilia treatment center (HTC) nurses who teach home infusion therapy (HIT).

Written and telephone interview surveys of the 153 nurses who teach HIT at federally funded HTCs.

Hemophilia treatment center nurses' teaching practices and infection control messages taught, and frequency of exposures to blood.

The response rate to the written nurses' survey was 60% and to the telephone interview 88%. Nurses taught patients a median of three HIT sessions totaling 4 hours of instruction. Reevaluation of patients' HIT practices took place every 6 months by 22% and every 12 months by 59% of nurses. Nurses frequently reported teaching proper use of a sharps disposal container (99%) and gloves (93%), but less often reported teaching patients to wash hands after infusions (26%) and to report needlestick injuries to HTCs (11%). The respondents identified several barriers to effective infection control as it is practiced in the home by patients. Although at least 30% of HTC nurses recalled having had percutaneous exposure to blood, they considered their risk for hepatitis B infection low but greater than for infection with the human immunodeficiency virus (HIV).

While some important infection control messages are stressed during HIT teaching, others may be underemphasized. Failure to instruct patients about all infection control precautions may be related to nurse educators' perception of low to moderate personal risk for hepatitis B and HIV infection. Patients receiving HIT, and those who assist them, need to be fully aware of, and to have reinforced periodically, universal infection control strategies in the home.

To determine risks for tuberculin skin-test conversion among employees of a community hospital in Ontario, Canada.

Cohort morbidity study.

Of 14 metropolitan Toronto area hospitals surveyed for data on tuberculin skin-test conversions, only one provided tuberculosis (TB) test data on all employees. Between 1991 and June 1994, 24 patients were treated at this hospital for pulmonary TB.

The population at risk included those on staff from January 1991 through December 1993 who previously were skin-test negative; they were followed until the end of June 1994. Exposure was estimated (a) based on ranking departments according to an estimate of the number of hours of direct patient contact during a typical day, and (b) based on location of sputum-positive patients.

Risks of skin-test conversion among hospital employees with documented prior negative skin tests.

A total of 809 skin-test negative employees were followed for 2,084 person-years; 18 employees with skin-test conversions were identitled. The overall conversion rate was 0.9% per year (0.86 per 100 person-years). After excluding two conversions attributed to contact with coworkers, the relative risk of conversion was 4.5 (5.5 after adjusting for age and gender) among those in the highest exposure category (≥4 hours per day), compared to those in departments ranked as having the lowest exposure (<2 hours per day). Among those working in wards in which sputum-positive patients were treated, 2.4% converted; the risk of conversion was over six times greater than among those working on wards with no TB patients or in departments with no patient contact, of whom 0.4% converted. Among the emergency room staff, the department in which the greatest number of sputum-positive patients were treated, at least 5% of staff converted. In those instances in which conversions were associated with exposure to a specific TB patient, the involved patients had been in the hospital for at least 4 days prior to being isolated.

These results indicate that even in a hospital with few admissions due to tuberculosis, skin-test conversions associated with occupational exposure may occur.

To study the loss of antimicrobial susceptibility in repeat (same patient, same bacterial species, and same site) aerobic gram-negative bacilli (AGNB) isolated from individual patients during their stay in the intensive-care unit (ICU).

A 792-bed, tertiary-care community hospital with a total of 107 adult, pediatric, and neonatal ICU beds. METHOD: An obser vational prospective study performed November 1992 through mid-July 1993.

Of 594 consecutive AGNB from 287 ICU patients, 117 isolates (20%) from 55 patients (19%) were repeat isolates, with the majority obtained from respiratory secretions (83%). Pseudomonas aeruginosa and Enterobacter species accounted for 61% of the isolates. Forty-two (36%) of the repeat isolates from 24 patients (44%) had >4-fold increase in minimum inhibitory concentration to at least one antibiotic and no longer were considered fully susceptible based on National Committee on Clinical Laboratory Standards criteria. Loss of antimicrobial susceptibility often developed within several (median 8) days and was associated only infrequently with simultaneous transition from colonization to infection in the individual patient. Use of certain β-lactam antibiotics was associated with increasing resistance to several other antibiotics in the same class. Concurrent use of β-lactams and aminoglycosides did not prevent loss of antimicrobial susceptibility to the former in repeat isolates.

We conclude that loss of antimicrobial susceptibility in repeat AGNB isolated from ICU patients is common, usually is not associated with transition from colonization to infection, and often is associated with prior use of antibiotics. Minimizing antibiotic use in ICU patients should help reduce the risk of antimicrobial resistance in repeat AGNB isolates.

To determine whether empiric isolation of patients with acute respiratory virus infection symptoms could be discontinued when preliminary shell vial cultures were negative, and the impact of this approach on hospital resources.

In 1993, we retrospectively reviewed respiratory virus test results from 1992 to 1993 and extended data collection prospectively through the 1993 to 1994 season. The rapid test and 48-hour shell vial results were compared to a standard of rapid test plus 5-day shell vial culture results to determine the sensitivity and specificity of these “preliminary” results.

A 400-bed tertiary referral research hospital.

Patients from any inpatient unit or clinic with acute respiratory virus infection symptoms who had a specimen submitted for respiratory virus culture. Patients were placed on empiric respiratory isolation pending culture results.

The overall sensitivity of the combined rapid and 48-hour culture results in adults and children was 97%. All 15 pediatric patients with respiratory syncytial virus infection who had specimens submitted on first suspicion of respiratory virus infection were positive by rapid test. Culture results were positive within 48 hours for 100% of patients with influenza A (15 patients), influenza B (6), and parainfluenza (18) viruses. Of 59 pediatric inpatients who were isolated empirically awaiting 5-day culture results, 31 (52%) ultimately were determined to be culture negative.

Empiric isolation of symptomatic children can be discontinued at 48 hours when both the rapid test and the early culture results are negative. Our institution would have saved 93 days of unnecessary isolation over 2 years had such a policy been in place.

To describe the epidemiology and the inter ventions used to control two methicillin-resistant Staphylococcus aureus (MRSA) epidemics involving 46 infants with two fatalities in a neonatal intensive care unit (NICU).

A 50-bed, level III NICU in a university hospital.

After traditional interventions failed to stop the first epidemic, an intensive microbiologic surveillance (IMS) program was developed. Cultures were obtained on all infants each week, and those colonized with MRSA were isolated. When an infant was found to be colonized with MRSA, cultures immediately were obtained on all surrounding infants. This was continued until no MRSA-colonized infants were found in the area. During the first epidemic, mupirocin was used in an attempt to eradicate the organism from the unit.

All infants, colonized and noncolonized, and parents of and personnel working with colonized infants were treated simultaneously with 5 days of mupirocin. This failed to eradicate MRSA in colonized infants. The spread of MRSA ceased in the unit, but a second epidemic occurred 4 months later. This time, IMS alone was successful in quickly containing the epidemic, and MRSA disappeared from the unit after all colonized infants were discharged. Plasmid analysis demonstrated that the same strain was responsible for both outbreaks.

IMS and isolation are effective in containing the spread of MRSA in an NICU. The use of mupirocin failed to eradicate the organism.