Prevalence of and Risk Factors for Methicillin-resistant Staphylococcus aureus (MRSA) in HIV Patients

By Liz Highleyman

MRSA is an aggressive skin infection that can affect humans.

Early this year, controversy arose after it was reported that gay men in San Francisco and Boston were disproportionately becoming infected with methicillin-resistant Staphylococcus aureus (MRSA).

MRSA is resistant to the major class of drugs used to treat this type of bacteria, and therefore it may progress rapidly and can be life-threatening. Transmitted via skin-to-skin contact, the risk of MRSA is not directly related to sexual orientation; outbreaks have also been reported, for example, among athletes and schoolchildren. But HIV positive people with compromised immune function may be particularly vulnerable.

As reported in the August 2008 Journal of Acquired Immune Deficiency Syndromes, U.S. researchers undertook a study to analyze the presence of MRSA in the noses of ambulatory HIV positive individuals seen at an HIV clinic; study participants were not hospital inpatients, a group that is highly susceptible to MRSA. Nasal colonization is not uncommon among healthy people who show no symptoms of infection.

A total of 146 HIV-infected individuals produced bilateral nasal and axillary (armpit) swabs. Specimens were plated on BBL CHROMagar MRSA media, molecular typing was done by pulse-field gel electrophoresis, and staphylococcal cassette chromosomemec typing was determined. Patients also completed questionnaires about potential MRSA risk factors and their medical records were reviewed.

Results

• 15 of 146 patients (10.3%) had MRSA nasal colonization.

• 1 of these individuals also had axillary colonization.

• 12 of 15 isolates were staphylococcal type IV, and 8 of 14 were genotype USA300 or USA400 (2 types commonly associated with community-based outbreaks).

• MRSA colonization was significantly associated with the following factors:

• History of prior MRSA or methicillin-susceptible Staphylococcus aureus infection (P < 0.05).

• Lower CD4 cell count (P < 0.05);

• Not receiving current or recent antibiotics (P < 0.05);

• There was a trend toward an association with hospitalization or an emergency department visit during the prior year (P = 0.064).

• Current use of trimethoprim-sulfamethoxazole (TMP-SMX; Bactrim, Septra) was protective against MRSA colonization.

• 0 of 29 TMP-SMX recipients were colonized with MRSA versus 15 of 117 (12.8%) non-recipients (P = 0.04).

• In a multivariate logistic regression model, the following factors remained associated with MRSA colonization:

• Prior infection with methicillin-susceptible Staphylococcus aureus (odds ratio [OR] 32.4);

• Prior infection with MRSA (OR 9.71);

• Lower CD4 count (OR 0.996);

• Not receiving current or recent antibiotics (OR 0.026).

Based on these findings, the researchers concluded that "The prevalence of MRSA nasal colonization was relatively high compared with prior studies," but "axillary colonization was rare."

"Prior staphylococcal infection (methicillin-susceptible S. aureus or MRSA), not receiving antibiotics, and lower CD4 count were associated with MRSA nasal colonization," they continued. "Trimethoprim-sulfamethoxazole seemed to be protective of MRSA colonization."

TMP-SMX is an antibiotic used to prevent certain AIDS-related opportunistic infections (OIs) in people with very low CD4 cell counts. It is not used as often in the HAART era, since people who receive antiretroviral therapy in a timely manner typically maintain a high enough CD4 count to avoid OIs. Prevention of MRSA infection may be one more argument in favor of prompt antiretroviral treatment.

Division of Infectious Diseases and Division of Pediatric Infectious Diseases, University of Texas Southwestern Medical Center, Dallas, TX; Casa Grande Regional Medical Center, Casa Grande, AZ; Division of Infectious Disease, Baystate Medical Center, Springfield, MA.

9/23/08

Reference
MJ Cenizal, RD Hardy, M Anderson, and others. Prevalence of and risk factors for methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization in HIV-infected ambulatory patients. Journal of Acquired Immune Deficiency Syndromes 48(5): 567-571. August 2008. (Abstract).