Infection with HIV per se does not increase the risk of colonisation with community-associated
MRSA, according to US research published in the online edition of Clinical Infectious Diseases.
The investigators found that prevalence of
nasal colonisation with community-associated MRSA (methicillin-resistant Staphylococcus aureus) was significantly
higher in HIV-positive patients compared to HIV-negative patients.
However, they also found a hierarchy of
risk among the HIV-positive patients. Moreover, after controlling for factors
such as imprisonment and area of residence, infection with HIV did not have a
significant association with MRSA colonisation.
“Community exposures may be more important
for predicting MRSA colonization than HIV status in certain groups,” comment
Earlier research by the same investigators
showed that HIV-positive patients had a six-fold higher risk of
community-acquired MRSA skin and soft tissue infections compared to
It is unclear why HIV-positive patients
have an increased risk of the infection. Immune
suppression and extensive use of antibiotics may be contributory factors.
But it is possible that factors beyond HIV
infection may also have a role. For instance, sexual contact has been
implicated in transmissions between gay men. Athletes also have a higher
prevalence of the infection, as do individuals who have been recently
Given this uncertainty, investigators
wished to establish a better understanding of the prevalence and risk factors
for colonisation with community-associated MRSA in different groups of patients
They therefore designed a study involving
458 HIV-positive patients, who received care at three different clinics, each
of which served the needs of individuals from different risk groups (women,
Hispanics, individuals recently released from incarceration). The study also
involved 143 HIV-negative patients who received treatment at a nearby
university hospital. The reseach was conducted between August 2010 and February
Overall, 9% of patients had nasal
colonisation with community-associated MRSA. This included 50 HIV-positive
patients (11%) and six of the HIV-negative patients (4%). The investigators
calculated that prevalence of MRSA colonisation was a significant 2.6 times
higher among HIV-positive patients compared to individuals who were
HIV-negative (p = 0.03).
Prevalence of colonisation with the
infection differed between the three groups of HIV-positive patients.
It was highest among those who had recently
been released from incarceration (16%), followed by HIV-infected women (12%).
Hispanic HIV-positive patients had the lowest prevalence of colonisation (3%).
Therefore, prevalence of MRSA colonisation
was almost six times higher among recently incarcerated patients compared to Hispanic
patients (p = 0.005). Prevalence of colonization was four times higher among
HIV-infected women compared to HIV-positive Hispanic patients (p = 0.015).
The investigators’ first set of analysis
showed that a number of factors increased the risk of colonization with MRSA.
These included ethnicity (African American and White vs. Hispanic, p = 0.013);
a prior history of MRSA infection (p = 0.033), a history of incarceration (p
< 0.001); living in specific “high risk” geographic areas (p = 0.17); and
infection with HIV (p = 0.016).
“CD4 cell count, [cotrimoxazole] prophylaxis, and
antiretroviral therapy were not significantly associated with MRSA colonization
among HIV-infected participants,” note the authors. This suggested to them that
“factors beyond immune suppression contribute to the higher colonization
“Multivariate” anaylsis that controlled for
potentially confounding factors continued to show an association between a
history of incarceration and colonization with MRSA (p = 0.03). There was also
a non-significant trend suggesting that area of residence was also a risk
factor (OR = 1.6; 95% CI, 0.92-3.0, p = 0.097). Hispanic ethnicity was
negatively associated with colonisation (p = 0.045).
After controlling for incarceration and
residence, infection with HIV ceased to have a significant association with
community-acquired MRSA colonization.
The investigators suggest “HIV status may
be a marker for exposure to high-risk social networks rather than being the
major factor contributing to high colonization and infection burden.”
They therefore conclude: “Social networks
may need to be examined for both HIV-positive and HIV-negative individuals
following release from correctional facilities into the community to
differentiate community risk factors for community-associated-MRSA and inform