The most common nosocomial Gram-positive species isolated in catheter-related bloodstream infections is Staphylococcus. Regional differences in the incidence of methicillin-resistant Staphylococcus aureus(MRSA) and coagulase-negative Staphylococcus (MR-CoNS) infections have been partly attributed to variation in antibiotic usage. Widespread use of vancomycin has also contributed to the emergence of vancomycin-resistant Staphylococcus aureus. Since antibiotic exposure and use vary among neonates(NICU), children (PICU), and adults (AdICU) in intensive care units, we determined whether differences in Staphylococcal infection rates and susceptibilities of MRSA and MR-CoNS infections exist.

Methods: Antibiotic susceptibility of nosocomial Staphylococcal infections in all ICUs within a 4-year period (1994-1997) at the University of Illinois Hospital were reviewed. Differences in the incidence rates and susceptibilities of MRSA and MR-CoNS were analyzed using t-test and chi-square. There were 413 Staphylococcal isolates from blood, cerebrospinal fluid, joint fluid, wound, and eye discharge within the intensive care units; 289 (70%) had sensitivities tested for methicillin, clindamycin, and tetracycline.

Results: The average yearly incidence of MRSA infections increased significantly between the NICU (11 ± 6%) and the PICU (20± 29%), p <0.05 and between the NICU and the AdICU (50 ± 6%), p <0.001. Staphylococcus aureus isolates susceptible to clindamycin were significantly higher in the NICU (92%) compared to the PICU (79%) and AdICU(52%), p <0.0001. Likewise, more MRSA isolates from the NICU (71%) were susceptible to clindamycin compared to the PICU (15%) and AdICU (7%), p<0.0001.

MR-CoNS was identified in 91% (range: 85-100%) of all CoNS isolates. MR-CoNS comprised 23% (range: 21-25%) of all CNS isolates per year among the ICUs. More CoNS and MR-CoNS isolates from the NICU were sensitive to clindamycin but were not significantly different from those isolated from PICU or AdICU. All Staphylococcal isolates were sensitive to tetracycline.

Conclusions: We conclude that more methicillin- and clindamycin-resistant Staphylococcus aureus infections are found in pediatric and adult patients as compared to neonates. This was not found with CoNS infections. Identification of the different Staphylococcal genotypes responsible for infections in different age groups may provide useful information in the search for alternative prophylactic and therapeutic antimicrobials especially in neonates.