Resistant Skin Infections in Gay Men in SF
I have had a couple people ask me about the article that was published early online from the February 19 issue of Annals of Internal Medicine (the Annals), describing an epidemiological study about an infection caused by community-acquired, multidrug-resistant, methicillin-resistant Staphylococcus aureus (CA MDR USA300) in men who have sex with men (MSM). So, I thought I'd make a quick post about it.
As background, methicillin-resistant Staphylococcus aureus (MRSA) has been a problematic organism for a number of years now. It is often the cause of skin and soft tissue infections (SSTIs) and is rapidly becoming the predominant strain of S. aureus cultured from these infections. Previously, S. aureus infections could be treated with a class of antibiotics called penicillinase-resistant penicillins or anti-staphylococcal penicillins, of which methicillin (Staphcillin; no longer available in the US) was a member. Community-acquired SSTIs caused by MRSA are commonly treated on an outpatient basis with oral sulfamethoxazole/trimethoprim (SMX/TMP), oral clindamycin, and/or topical mupirocin. However, in certain cases, these drugs may have difficulty penetrating the tissue at the infection site. More serious MRSA infections are treated with intravenous vancomycin. As with any infection, if left untreated or improperly treated, MRSA can be limb- and life-threatening.
CA MDR USA300 is a newly-emerging strain of MRSA that is resistant to more classes of antibiotics, including clindamycins and mupirocin. It remains susceptible to SMX/TMP and vancomycin.
According to the study published in the Annals, CA MDR USA300 infection has been observed to be more common in MSM. Many of these infections involve the buttocks, genitals, and perineum. Other independent risk factors for developing the infections include MRSA infection, clindamycin use, or mupirocin use in the past 12 months.
Unfortunately, the study did not include a control group of men who do not have sex with men. Thus, it is difficult to say that the actual act of homosexual sex is a risk factor, itself. Since S. aureus is not a gut flora, it is unlikely that anal sex specifically increases the risk of CA MDR USA300 infection, unless it is skin-abrading. However, MSM generally have more frequent sex with more partners than do men who do not have sex with men. These factors, along with illicit drug use, group sex, skin-abrading sex, and history of sexually-transmitted infections (STIs), including HIV, are more common in MSM and may be the actual cause for the increased risk in this population. Since the study was retrospective, there may be other risk factors that could not be screened.
A major portion of this study was conducted in San Francisco (along with Boston) with 2004-2006 data. The highest incidence of CA MDR USA300 (170 cases/100,000 persons) was found to be in persons residing in the 94114 ZIP code, which includes the Castro district.
Although condom use is always recommended to prevent the spread of other STIs, SSTIs are not generally prevented by condom use, since it is passed directly from skin to skin, not requiring bodily fluid exchange. Therefore, care should be taken to limit the known risk factors listed above. In addition, I would advise against the use of clindamycin or mupirocin as empiric (initial) treatment of SSTIs in patients at high risk for CA MDR USA300 until culture and sensitivity data can be acquired showing susceptibility of the organism to those agents. SMX/TMP can still be used with a fair amount of confidence in patients with milder SSTIs. Vancomycin is generally recommended in patients with more serious or hospital-acquired SSTIs.
As background, methicillin-resistant Staphylococcus aureus (MRSA) has been a problematic organism for a number of years now. It is often the cause of skin and soft tissue infections (SSTIs) and is rapidly becoming the predominant strain of S. aureus cultured from these infections. Previously, S. aureus infections could be treated with a class of antibiotics called penicillinase-resistant penicillins or anti-staphylococcal penicillins, of which methicillin (Staphcillin; no longer available in the US) was a member. Community-acquired SSTIs caused by MRSA are commonly treated on an outpatient basis with oral sulfamethoxazole/trimethoprim (SMX/TMP), oral clindamycin, and/or topical mupirocin. However, in certain cases, these drugs may have difficulty penetrating the tissue at the infection site. More serious MRSA infections are treated with intravenous vancomycin. As with any infection, if left untreated or improperly treated, MRSA can be limb- and life-threatening.
CA MDR USA300 is a newly-emerging strain of MRSA that is resistant to more classes of antibiotics, including clindamycins and mupirocin. It remains susceptible to SMX/TMP and vancomycin.
According to the study published in the Annals, CA MDR USA300 infection has been observed to be more common in MSM. Many of these infections involve the buttocks, genitals, and perineum. Other independent risk factors for developing the infections include MRSA infection, clindamycin use, or mupirocin use in the past 12 months.
Unfortunately, the study did not include a control group of men who do not have sex with men. Thus, it is difficult to say that the actual act of homosexual sex is a risk factor, itself. Since S. aureus is not a gut flora, it is unlikely that anal sex specifically increases the risk of CA MDR USA300 infection, unless it is skin-abrading. However, MSM generally have more frequent sex with more partners than do men who do not have sex with men. These factors, along with illicit drug use, group sex, skin-abrading sex, and history of sexually-transmitted infections (STIs), including HIV, are more common in MSM and may be the actual cause for the increased risk in this population. Since the study was retrospective, there may be other risk factors that could not be screened.
A major portion of this study was conducted in San Francisco (along with Boston) with 2004-2006 data. The highest incidence of CA MDR USA300 (170 cases/100,000 persons) was found to be in persons residing in the 94114 ZIP code, which includes the Castro district.
Although condom use is always recommended to prevent the spread of other STIs, SSTIs are not generally prevented by condom use, since it is passed directly from skin to skin, not requiring bodily fluid exchange. Therefore, care should be taken to limit the known risk factors listed above. In addition, I would advise against the use of clindamycin or mupirocin as empiric (initial) treatment of SSTIs in patients at high risk for CA MDR USA300 until culture and sensitivity data can be acquired showing susceptibility of the organism to those agents. SMX/TMP can still be used with a fair amount of confidence in patients with milder SSTIs. Vancomycin is generally recommended in patients with more serious or hospital-acquired SSTIs.