[Emerging Infectious Diseases * Volume 4 * Number 1 * January - March 1998] Dispatches Laboratory Survey of Drug-Resistant _Streptococcus pneumoniae_ in New York City, 1993—1995 Richard Heffernan, Kelly Henning, Anne Labowitz, Annette Hjelte, and Marcelle Layton New York City Department of Health, New York, New York, USA --------------------------------------------------------------------------- Wide geographic variation in the prevalence of drug-resistant _Streptococcus pneumoniae_ demonstrates the importance of tracking antimicrobial resistance locally. This survey of hospital microbiology laboratories in New York City found that penicillin resistance (MIC >/= 2.0 mg/ml) increased from 1.5% of _S. pneumoniae_ isolates in 1993 to 6.3% in 1995 and that in 1995, one-third of isolates nonsusceptible to penicillin (MIC >/= 0.1 µg/ml) were also nonsusceptible to an extended-spectrum cephalosporin (MIC >/= 1 µg/ml). The emergence of drug-resistant _Streptococcus pneumoniae_ underscores the need for timely, local, population-based surveillance of antimicrobial resistance. The prevalence of resistance in U.S. communities varies widely, with 2% to 53% of _S. pneumoniae_ isolates found to have reduced susceptibility to penicillin (1-4). The Centers for Disease Control and Prevention recommends that empiric antibiotic therapy for pneumococcal infections be based upon local susceptibility patterns (2,5). However, few communities track drug-resistant _S. pneumoniae_. The Survey To estimate the prevalence of drug-resistant _S. pneumoniae_ in New York City, we surveyed hospital-based clinical microbiology laboratories from 1993 to 1995. A standardized questionnaire was mailed annually to each laboratory, and those that did not respond were contacted by telephone or were visited. To evaluate compliance with _S. pneumoniae_ penicillin susceptibility testing guidelines established by the National Committee for Clinical Laboratory Standards (NCCLS) (6), we asked about criteria for selecting specimens and techniques for oxacillin disk diffusion screening and determination of penicillin MICs. To determine the prevalence of penicillin resistance, we asked for the number of _S. pneumoniae_ isolates identified during the year, the number tested for susceptibility to penicillin, and the number found to be possibly resistant by the oxacillin disk diffusion test and penicillin-intermediate or -resistant by MIC testing. We also asked that information be provided separately for isolates from normally sterile sites (e.g., blood, cerebrospinal fluid) and from nonsterile sites (e.g., sputum, nasopharyngeal swab). In 1995, we added questions regarding the MIC test results for extended-spectrum cephalosporins (ESCs), including the number of penicillin-nonsusceptible isolates that were also nonsusceptible to an ESC. No individual patient information was obtained. A report summarizing the results of the survey and describing NCCLS guidelines was mailed annually to microbiology laboratories, hospital infection control departments, and local infectious disease physicians and pediatricians. Analysis Of 67 hospital-based clinical microbiology laboratories in New York City, 100% completed the survey in 1993, 98% in 1994, and 100% in 1995. Overall, more than 5,000 _S. pneumoniae_ isolates were reported annually. Data were analyzed by using EpiInfo Version 6.0 (CDC, Atlanta, GA, USA). Drug-susceptibility results are presented for laboratories that conformed with NCCLS guidelines and provided complete data on all _S. pneumoniae_ isolates identified (Table 1). Table 1. Penicillin resistance among _Streptococcus pneumoniae_ isolates at New York City hospital laboratories --------------------------------------------------------------------------- No. of isolates 1993 1994 1995 No. (%) No. (%) No. (%) ------------------------------------------------------------------ Screened with oxacillin disk (sup 3,227 4,133 4,912 a) zone size /= 0.1 and /= 2.0 µg/ml). (sup e)Number of laboratories reporting sterile site isolate results in 1993, 1994, 1995 was 8, 12, 32, respectively. (sup f)Number of laboratories reporting nonsterile site isolate results in 1993, 1994, 1995 was 5, 9, 28, respectively. --------------------------------------------------------------------------- Susceptibility Criteria The NCCLS recommends routine screening by the oxacillin disk diffusion test of clinically important _S. pneumoniae_ isolates for susceptibility to penicillin. Isolates with a zone size /= 0.1 and /= 2 µg/ml) should also have MICs determined for susceptibility to an ESC such as cefotaxime or ceftriaxone (ESC-intermediate MIC = 1 µg/ml; ESC-resistant MIC >/= 2 µg/ml) (6). We will use the term "nonsusceptible" to refer to both intermediate and resistant isolates. Findings The proportion of laboratories conforming with NCCLS guidelines for penicillin susceptibility testing of _S. pneumoniae_ increased from 22% in 1993 to 69% in 1995. This was due to an increase in the number of laboratories that screened all isolates, a sharp decrease in the use of automated MIC tests, and a fourfold rise in the use of antibiotic gradient strips for determining MICs (Table 2). Overall, the proportion of isolates with oxacillin disk diffusion test zone size