Paola C. DeGirolami

Clinical and molecular epidemiology of sporadic and clustered cases of nosocomial Clostridium difficile diarrhea

PURPOSE A prospective clinical and molecular epidemiologic study was conducted to define the frequency of nosocomial Clostridium difficile patient-to-patient transmission in an urban tertiary referral hospital. PATIENTS AND METHODS Over a 6-month period, environmental cultures for C difficile were obtained from patients with new positive stool cytotoxin assay (index cases); stool samples were obtained from selected patient contacts (the roommate, occupants of adjacent rooms, and the patient occupying the index room after discharge of the index case); and hand cultures were obtained from personnel contacts. C difficile isolates were analyzed by pulse-field gel electrophoresis (PFGE) or, for isolates that were nontypeable by PFGE, by restriction enzyme analysis. RESULTS During the study period, we identified 98 index cases of C difficile toxin-associated diarrhea, including focal outbreaks on two wards totaling 26 cases within a 2-month interval. Environmental contamination was detected at > or = 1 sites in 58% of rooms and often involved wide dispersed areas. Among 99 prospectively identified patient contacts, C difficile was cultured from the stool of 31 (31%), including 12 with diarrhea and 19 who were asymptomatic. C difficile was cultured from the hands of 10 (14%) of 73 personnel. Molecular analysis resolved 31 typing profiles among the index isolates; the most common profile (designated strain D1) was represented by 30 isolates. Among the isolates from patient contacts, 5 of 12 from symptomatic contacts matched the corresponding index isolate, and only 1 of 19 from asymptomatically colonized contacts matched. Transmission to personnel or patient contacts of the strain cultured from the corresponding index case was correlated strongly with the intensity of environmental contamination. Strain D1 was frequently represented among isolates associated with heavy environmental contamination, with personnel carriage, and with development of symptomatic illness among prospectively identified contacts. CONCLUSIONS Intense environmental contamination and transmission to close personnel and patient contacts represented coordinated properties of an individual epidemic strain. For most epidemiologically linked contacts, positive cultures for C difficile did not result from transmission from the presumed index case.

Epidemics of Diarrhea Caused by a Clindamycin-Resistant Strain of Clostridium difficile in Four Hospitals

BACKGROUND Large outbreaks of diarrhea caused by a newly recognized strain of Clostridium difficile occurred in four hospitals located in different parts of the United States between 1989 and 1992. Since frequent use of clindamycin was associated with the outbreak in one of the hospitals, we examined the resistance genes of the epidemic-strain isolates and studied the role of clindamycin use in these outbreaks. METHODS Case-control studies were performed at three of the four hospitals to assess the relation of the use of clindamycin to C. difficile-associated diarrhea. All isolates of the epidemic strain and representative isolates of other strains identified during each outbreak were tested for susceptibility to clindamycin. Chromosomal DNA from these representative isolates was also analyzed by dot blot hybridization and amplification with the polymerase chain reaction (PCR) with the use of probes and primers from a previously described determinant of erythromycin resistance - the erythromycin ribosomal methylase B (ermB) gene - found in C. perfringens and C. difficile. RESULTS In a stratified analysis of the case-control studies with pooling of the results according to the Mantel-Haenszel method, we found that the use of clindamycin was significantly increased among patients with diarrhea due to the epidemic strain of C. difficile, as compared with patients whose diarrhea was due to nonepidemic strains (pooled odds ratio, 4.35; 95 percent confidence interval, 2.02 to 9.38; P<0.001). Exposure to other types of antibiotics or hospitalization in a surgical ward was not significantly associated with the risk of C. difficile-associated diarrhea due to the epidemic strain. All epidemic-strain isolates were highly resistant to clindamycin (minimal inhibitory concentration, >256 microg per milliliter). DNA hybridization and PCR analysis showed that all these isolates had an ermB gene, which encodes a 23S ribosomal RNA methylase that mediates resistance to macrolide, lincosamide, and streptogramin antibiotics. Only 15 percent of the nonepidemic strains were resistant to clindamycin. CONCLUSIONS A strain of C. difficile that is highly resistant to clindamycin was responsible for large outbreaks of diarrhea in four hospitals in different states. The use of clindamycin is a specific risk factor for diarrhea due to this strain. Resistance to clindamycin further increases the risk of C. difficile-associated diarrhea, an established complication of antimicrobial use.

Linezolid Resistance in Sequential Staphylococcus aureus Isolates Associated with a T2500A Mutation in the 23S rRNA Gene and Loss of a Single Copy of rRNA

Linezolid is an important therapeutic option for infections caused by resistant gram-positive bacteria. We report the characterization of sequential methicillin-resistant Staphylococcus aureus (MRSA) bloodstream isolates that developed resistance in a patient treated with a prolonged course of linezolid. Analysis of this series of clinical MRSA isolates detected, in the resistant isolates, the presence of a T2500A mutation in the domain V region of the 23S rRNA gene. In addition, the loss of a single copy of the 23S rRNA gene was found in 2 of the resistant isolates. As a result of these 2 factors, the proportion of mutant : wild-type 23S rRNA genes increased in association with an increase in the minimum inhibitory concentration of linezolid. The most recent isolate of this series was recovered 7 months after the patient discontinued linezolid and demonstrated reversion to a susceptible phenotype associated with a loss of the T2500A mutation.

Staphylococcus aureus Accessory Gene Regulator (agr) Group II: Is There a Relationship to the Development of Intermediate-Level Glycopeptide Resistance?

We previously determined that all 6 Staphylococcus aureus strains with confirmed intermediate-level resistance to glycopeptides (glycopeptide intermediate S. aureus [GISA]) from the United States that we tested belonged to accessory gene regulator (agr) group II. In the present study, we found that 56% of surveyed bloodstream methicillin-resistant S. aureus isolates (n = 148) at our hospital were agr group II, whereas only 24% of methicillin-susceptible S. aureus isolates (n = 33) were agr group II (P = .001). Population analysis of genetically engineered agr-null and parent wild-type strains of groups I, II, and IV revealed that, when agr function is lost, the agr group II knockout S. aureus was most likely to develop glycopeptide heteroresistance after growth in 1 microg/mL but not 16 microg/mL vancomycin. This strain was unique in showing decreased autolysis after growth in these conditions. This study suggests that some S. aureus strains have an intrinsic survival advantage under a glycopeptide selective pressure, which is possibly related to reduced autolysis after exposure to subinhibitory concentrations of glycopeptide.

Methicillin-Resistant Staphylococcus aureus: Comparison of Susceptibility Testing Methods and Analysis of mecA-Positive Susceptible Strains

ABSTRACT Methicillin-resistant Staphylococcus aureus (MRSA) is responsible for an increasing number of serious nosocomial and community-acquired infections. Phenotypic heterogeneous drug resistance (heteroresistance) to antistaphylococcal beta-lactams affects the results of susceptibility testing. The present study compared the MRSA-Screen latex agglutination test (Denka Seiken Co., Ltd., Tokyo, Japan) for detection of PBP 2a with agar dilution, the VITEK-1 and VITEK-2 systems (bioMérieux, St. Louis, Mo.), and the oxacillin agar screen test for detection of MRSA, with PCR for themecA gene used as the “gold standard” assay. Analysis of 107 methicillin-susceptible S. aureus (MSSA) isolates and 203 MRSA isolates revealed that the MRSA-Screen latex agglutination test is superior to any single phenotype-based susceptibility testing method, with a sensitivity of 100% and a specificity of 99.1%. Only one isolate that lacked mecAwas weakly positive by the MRSA-Screen latex agglutination test. This isolate was phenotypically susceptible to oxacillin and did not contain the mecA gene by Southern blot hybridization. The oxacillin agar screen test, the VITEK-1 system, the VITEK-2 system, and agar dilution showed sensitivities of 99.0, 99.0, 99.5, and 99%, respectively, and specificities of 98.1, 100, 97.2, and 100%, respectively. The differences in sensitivity or specificity were not statistically significant. Oxacillin bactericidal assays showed thatmecA- and PBP 2a-positive S. aureusisolates that are susceptible to antistaphylococcal beta-lactams by conventional methods are functionally resistant to oxacillin. We conclude that the accuracy of the MRSA-Screen latex agglutination method for detection of PBP 2a approaches the accuracy of PCR and is more accurate than any susceptibility testing method used alone for the detection of MRSA.

Epidemiology and Clinical Outcomes of Patients with Multiresistant Pseudomonas aeruginosa

We conducted a case-series study of multiresistant Pseudomonas aeruginosa in patients who did not have cystic fibrosis. Patient characteristics, antibiotic exposures, time course of emergence of resistance, and clinical outcomes were examined. Twenty-two patients were identified from whom P. aeruginosa resistant to ciprofloxacin, imipenem, ceftazidime, and piperacillin was isolated. Nineteen (86%) had clinical infection. Patients received prolonged courses of antipseudomonal antibiotics before isolation of multiresistant P. aeruginosa. Nine of 11 patients with soft-tissue infection exhibited resolution of clinical infection but usually required surgical removal of infected tissue with or without revascularization. Overall, three patients died. In two instances in which multiple isolates with different susceptibility profiles from the same patient were available, pulsed-field gel electrophoresis profiles of serial isolates were indistinguishable or closely related. This study illustrates that multiresistant P. aeruginosa emerges in a stepwise manner after exposure to antipseudomonal antibiotics and results in adverse outcomes.

Carriage of Methicillin-Resistant Staphylococcus Aureus at Hospital Admission

OBJECTIVES To measure the prevalence of, and to establish predictors for, the nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) at hospital admission. To evaluate mannitol-salt agar with oxacillin for the simultaneous detection and identification of MRSA from nasal swabs. DESIGN Three-month prospective case-control survey, with data collected from interviews and computerized databases. The criterion standard for MRSA detection was culture on Mueller-Hinton agar with oxacillin 6 microg/mL (National Committee for Clinical Laboratory Standards method). SETTING 320-bed tertiary-care hospital. PATIENTS 387 patients screened within 24 hours after admission, including 10 MRSA carriers (cases), 291 patients with no S aureus, and 86 patients with methicillin-susceptible S aureus. RESULTS The prevalence of MRSA nasal carriage was 2.6%, whereas the prevalence of carriage was 3.1% when both nasal and wound cultures were performed. The significant predictors of carriage were a prior detection of MRSA, open wounds, diabetes mellitus, treatments by injection, prior nursing home stays, visits at home by a nurse, and prior antibiotic treatments. Cases had stayed for longer periods in hospitals and had received longer antibiotic treatments within a year. Eighty patients (including the 10 cases) had diabetes, had been exposed to healthcare facilities within a year, and had antibiotics within 6 months. The sensitivity and negative predictive value of nasal swabs on mannitol-salt agar with oxacillin were 60% and 71%, respectively. CONCLUSION MRSA carriage on admission to the hospital may be an increasing and underestimated problem. Further studies are needed to develop and validate a sensitive and specific prediction rule.

An Outbreak of Rubella among Hospital Personnel

An outbreak of 47 cases of rubella occurred among hospital personnel in a large medical-surgical hospital. As a result, one pregnancy was terminated and 475 employee workdays were lost. Epidemiologic investigation of the outbreak suggested a common source; a dietary worker was identified as the probable index case. Serum samples of 12 per cent of women employees were negative for rubella antibody at the time of the outbreak. Neither a history of rubella nor a history of immunization with rubella vaccine was reliable in the prediction of the presence or absence of immunity. Two thirds of all hospital personnel were immunized through a voluntary mass-immunization program, but the response of physicians to the program was disappointing. Outbreaks of rubella that occur in hospitals with prenatal clinics are of special concern. Testing of all employees for rubella antibody and immunization of those determined to be seronegative should be considered.

Colonization with broad-spectrum cephalosporin-resistant gram-negative bacilli in intensive care units during a nonoutbreak period: prevalence, risk factors, and rate of infection.

OBJECTIVE To define the epidemiology of broad-spectrum cephalosporin-resistant gram-negative bacilli in intensive care units (ICUs) during a nonoutbreak period, including the prevalence, the risk factors for colonization, the frequency of acquisition, and the rate of infection. DESIGN Prospective cohort study. SETTING Tertiary care hospital. PATIENTS Consecutive patients admitted to two surgical ICUs. MAIN OUTCOME MEASUREMENTS Serial patient surveillance cultures screened for ceftazidime (CAZ) resistance, antibiotic and hospital exposure, and infections. RESULTS Of the 333 patients enrolled, 60 (18%) were colonized with CAZ-resistant gram-negative bacilli (CAZ-RGN) at admission. Clinical cultures detected CAZ-RGN in only 5% (3/60) of these patients. By using logistic regression, CAZ-RGN colonization was associated with duration of exposure to cefazolin (odds ratio, 10.3; p < or = .006) and to broad-spectrum cephalosporins/penicillins (odds ratio, 2; p < or = .03), Acute Physiology and Chronic Health Evaluation III score (odds ratio, 1.2; p < or = .008), and previous hospitalization (odds ratio, 3.1; p < or = .006). Of the 100 patients who remained in the surgical ICU for > or = 3 days, 26% acquired a CAZ-RGN. Of the 14 infections caused by CAZ-RGN, 11 (79%) were attributable to the same species present in surveillance cultures at admission to the surgical ICU. CONCLUSIONS Colonization with CAZ-RGN was common and was usually not recognized by clinical cultures. Most patients colonized or infected with CAZ-RGN had positive surveillance cultures at the time of admission to the surgical ICU, suggesting that acquisition frequently occurred in other wards and institutions. Patients exposed to first-generation cephalosporins, as well as broad-spectrum cephalosporins/penicillins, were at high risk of colonization with CAZ-RGN. Empirical treatment of nosocomial gram-negative infections with broad-spectrum cephalosporins, especially in the critically ill patient, should be reconsidered.

Multicenter Typing Comparison of Sporadic and Outbreak Clostridium difficile Isolates from Geographically Diverse Hospitals

In a collaborative study by three laboratories, arbitrarily primed polymerase chain reaction (AP-PCR), HindIII restriction enzyme analysis (REA), and pulsed-field gel electrophoresis (PFGE) using SmaI were compared for typing of Clostridium difficile. The study included 30 isolates from nosocomial outbreaks in six geographically disparate hospitals and 15 isolates from sporadic cases of C. difficile diarrhea. REA distinguished a total of 23 types representing 10 groups; AP-PCR performed at Deaconess Hospital resolved 19 types; AP-PCR performed at the Centers for Disease Control resolved 15 types. Thirty isolates exhibited degradation of larger sized fragments during processing and therefore were nontypeable by PFGE; among the remaining 15 isolates, PFGE resolved 11 types. Outbreak isolates in five different hospitals represented REA group J and constituted a single AP-PCR strain. In summary, nosocomial outbreaks of C. difficile diarrhea in five hospitals were associated with a single genetic lineage as resolved by multiple strain typing systems.