Methicillin-resistant Staphylococcus aureus (MRSA) carriage and subsequent infection were prospectively compared among a well-defined group of 107 individuals infected with human immunodeficiency virus type 1 (HIV-1) who had no evidence of immune suppression and 52 epidemiologically matched, uninfected individuals. The carriage strains and infecting strains were genetically characterized. The cumulative prevalence of MRSA carriage was significantly higher among HIV-infected individuals (16.8%) than among individuals without HIV infection (5.8%) (P = .04; odds ratio, 3.3 [95% confidence interval, 1.3-14.7]). Fifteen of 21 MRSA isolates recovered from colonized individuals were identified as strain USA300. Of the 10 MRSA skin and soft tissue infections observed in this study, all occurred in HIV-infected individuals who were colonized with the same strain that caused the infection. Previous antibiotic use was the only statistically significant risk factor for MRSA carriage. These data highlight the fact that MRSA colonization and infection are important clinical issues among asymptomatic HIV-1-infected individuals.

The clinical relevance of Acinetobacter species, other than A. baumannii, as human pathogens has not been sufficiently assessed owing to the insufficiency of simple phenotypic clinical diagnostic laboratory tests. Infections caused by these organisms have different impacts on clinical outcome and require different treatment and management approaches. It is therefore important to correctly identify Acinetobacter species. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has been introduced to identify a wide range of microorganisms in clinical laboratories, but only a few studies have examined its utility for identifying Acinetobacter species, particularly those of the non-Acinetobacter baumannii complex. We therefore evaluated MALDI-TOF MS for identification of Acinetobacter species by comparing it with sequence analysis of rpoB using 123 isolates of Acinetobacter species from blood. Of the isolates examined, we identified 106/123 (86.2%) to species, and 16/123 (13.0%) could only be identified as acinetobacters. The identity of one isolate could not be established. Of the 106 species identified, 89/106 (84.0%) were confirmed by rpoB sequence analysis, and 17/106 (16.0%) were discordant. These data indicate correct identification of 89/123 (72.4%) isolates. Surprisingly, all blood culture isolates were identified as 13 species of Acinetobacter, and the incidence of Acinetobacter pittii was unexpectedly high (42/123; 34.1%) and exceeded that of A. baumannii (22/123; 17.9%). Although the present identification rate using MALDI-TOF MS is not acceptable for species-level identification of Acinetobacter, further expansion of the database should remedy this situation.

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