Perianal infection with MRSA is associated with an increased risk of developing skin and soft tissue infections, US investigators report in a study published in the online edition of Clinical Infectious Diseases. They also found that skin and soft tissue infections appeared to be linked to sexual activity, supporting the hypothesis that the infection is spread through skin-to-skin contact. HIV-positive men were more likely to develop skin and soft tissue infections than HIV-negative men.
Community-acquired methicillin-resistant Staphylococcus aureus (MRSA) is increasingly being recognised as an important source of skin and soft tissue infections.
Earlier research in gay men found that the infection is linked to multiple anonymous sex partners and the use of illicit drugs. HIV-positive gay men have been shown to be at increased risk of MRSA, with a low CD4 cell count and high viral load being risk factors.
Nasal infection with MRSA has been well described, but as many as 20% of infections involve perineal infection. As a significant proportion of patients with MRSA develop buttock and groin infections, it has been hypothesised that perineal infection contributes to the development of MRSA-associated skin and soft tissue infections in this region. (The investigators use the terms `perineal` and `perianal` interchangeably).
Investigators from Boston wished to gain a better understanding of the contribution of nasal and perineal infection with MRSA to the development of skin and soft tissue infections. They also wished to determine the behaviour and demographic risk factors.
They therefore designed a study involving 795 patients of Fenway Community Health in Boston. A significant proportion of this facility’s patients are gay men, many of whom are HIV-positive.
Between October 2005 and January 2007 patients had swabs taken from their nasal passages, perianal region, and open wounds which there then analysed for MRSA infection. They were then followed for one year to monitor to the development of skin and soft tissue infections.
A total of 547 (70%) of the study participants were gay men and a third of the entire sample was HIV-positive.
MRSA was identified in 30 patients (4%). It was present in the nasal passages in 26 patients, the perianal region in twelve individuals, and in the wounds of five individuals.
Skin and soft tissue infections were present in 29 (4%) of patients at baseline and a further 72 (9%) individuals developed such infections during follow up.
Culture specimens were obtained from the infections of 41 individuals, and 22 of these showed evidence of MRSA infection. The most common site for these infections was the lower extremities (30%).
The presence of MRSA at baseline in the nose (OR, 4.81; 95% CI, 1.73-12.13), perianal region (OR, 14.86; 95% CI, 3.90-60.64), or wounds (OR, 15.4; 95% CI, 1.72-186.1) were all strongly associated with the development of skin and soft tissue infections.
Indeed, 37% of those with MRSA at baseline developed such infections compared to 8% of individuals who were MRSA free (p
HIV-positive individuals were more likely to develop skin and soft tissue infections (p
A number of behavioural characteristics were strongly associated with the development of skin and soft tissue infections. These included sex with men (p = 0.02), anal sex (p
In statistical analysis that controlled for potential confounding factors, perianal infection with MRSA (but not nasal infection) remain associated with the development of skin and soft tissue infections (OR, 10.34; 95% CI, 2.84-37.6), as did the use of methamphetamine (OR, 4.98; 95% CI, 2.60-9.55).
The investigators describe the association between peianal MRSA infection and the development of skin and soft tissue infections as “intriguing.” Furthermore, the findings showing that sexual behaviour and drug use were associated with skin and soft tissue infections ‘lend strength to the hypothesis that skin-skin contacts are important for community-acquired MRSA transmission.”
They conclude that only screening patients for MRSA infection with nasal swabs is likely to mean that a significant number of infections remain unrecognised.
Szumowski JD et al. Methicillin-resistant Staphylococcus aureus colonization, behavioral risk factors, and skin and soft-tissue infection at an ambulatory clinic serving a large population of HIV-infected men who have sex with men. Clin Infect is 49 (online edition), 2009.