Illicit drug use and risk for USA300 methicillin-resistant Staphylococcus aureus infections with bacteremia

Methicillin-resistant staphylococci: implications for our food supply?

Food-borne intoxication, caused by heat-stable enterotoxins produced by Staphylococcus aureus, causes over 240,000 cases of food-borne illness in the United States annually. Other staphylococci commonly associated with animals may also produce these enterotoxins. Foods may be contaminated by infected food handlers during slaughter and processing of livestock or by cross-contamination during food preparation. S. aureus also causes a variety of mild to severe skin and soft tissue infections in humans and other animals. Antibiotic resistance is common in staphylococci. Hospital-associated (HA) S. aureus are resistant to numerous antibiotics, with methicillin-resistant S. aureus (MRSA) presenting significant challenges in health care facilities for over 40 years. During the mid-1990s new human MRSA strains developed outside of hospitals and were termed community-associated (CA). A few years later, MRSA was isolated from horses and methicillin resistance was detected in Staphylococcus intermedius/pseudintermedius from dogs and cats. In 2003, a livestock-associated (LA) MRSA strain was first detected in swine. These methicillin-resistant staphylococci pose additional food safety and occupational health concerns. MRSA has been detected in a small percentage of retail meat and raw milk samples indicating a potential risk for food-borne transmission of MRSA. Persons working with animals or handling meat products may be at increased risk for antibiotic-resistant infections. This review discusses the scope of the problem of methicillin-resistant staphylococci and some strategies for control of these bacteria and prevention of illness.

Community-associated methicillin-resistant Staphylococcus aureus bacteremia and endocarditis among HIV patients: a cohort study

BACKGROUND

HIV patients are at increased risk of development of infections and infection-associated poor health outcomes. We aimed to 1) assess the prevalence of USA300 community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) among HIV-infected patients with S. aureus bloodstream infections and. 2) determine risk factors for infective endocarditis and in-hospital mortality among patients in this population.

METHODS

All adult HIV-infected patients with documented S. aureus bacteremia admitted to the University of Maryland Medical Center between January 1, 2003 and December 31, 2005 were included. CA-MRSA was defined as a USA 300 MRSA isolate with the MBQBLO spa-type motif and positive for both the arginine catabolic mobile element and Panton-Valentin Leukocidin. Risk factors for S. aureus-associated infective endocarditis and mortality were determined using logistic regression to calculate odds ratios (OR) and 95% confidence intervals (CI). Potential risk factors included demographic variables, comorbid illnesses, and intravenous drug use.

RESULTS

Among 131 episodes of S. aureus bacteremia, 85 (66%) were MRSA of which 47 (54%) were CA-MRSA. Sixty-three patients (48%) developed endocarditis and 10 patients (8%) died in the hospital on the index admission Patients with CA-MRSA were significantly more likely to develop endocarditis (OR = 2.73, 95% CI = 1.30, 5.71). No other variables including comorbid conditions, current receipt of antiretroviral therapy, pre-culture severity of illness, or CD4 count were significantly associated with endocarditis and none were associated with in-hospital mortality.

CONCLUSIONS

CA-MRSA was significantly associated with an increased incidence of endocarditis in this cohort of HIV patients with MRSA bacteremia. In populations such as these, in which the prevalence of intravenous drug use and probability of endocarditis are both high, efforts must be made for early detection, which may improve treatment outcomes.

USA300 methicillin-resistant S. aureus (USA300 MRSA) colonization and the risk of MRSA infection in residents of extended-care facilities

To examine the pathogenesis of USA300 MRSA infection in long-term care residents, we performed a retrospective cohort study of 1691 adult residents of two extended-care facilities from 2003 to 2007 to assess whether the risk of subsequent MRSA infection is higher in USA300 MRSA-colonized residents compared to non-colonized residents or non-USA300 MRSA colonized residents. Six per cent of residents were colonized with USA300 MRSA; 12% of residents were colonized with non-USA300 MRSA; and 101 residents developed MRSA infection. The risk of infection was twofold higher in residents colonized with USA300 MRSA compared to residents not colonized with MRSA [adjusted hazard ratio 2·3, 95% confidence interval (CI) 1·1-4·5]. The risk of infection in USA300 MRSA-colonized residents was similar to USA300 MRSA non-colonized residents (relative risk 1·1, 95% CI 0·5-2·3). Our findings show that colonization with USA300 MRSA increases the risk of MRSA infection suggesting a similar pathogenesis.