Patients newly colonized with methicillin-resistant Staphylococcus aureus (MRSA) are at higher risk of clinical MRSA infection. At present, there are limited data on the duration or magnitude of this risk in a hospital population with a known time of MRSA acquisition.
Balm, et al. (2013) reported on a retrospective cohort study of 909 adult patients known to have newly identified MRSA colonization during admission to National University Hospital, Singapore that was undertaken between July 1, 2007 and June 30, 2011. Patients were excluded if they had history of previous MRSA colonization or infection, or if they had been a hospital inpatient in the preceding 12 months. Data were collected on the development of MRSA infection requiring hospitalization up to June 30, 2012.
Of 840 patients newly colonized with MRSA as identified on active surveillance and not clinical specimens, 546 were men (65.0 percent) and the median age was 65 years (range 18-103 years). Median follow up was 24 months (range 0-64 months, 85.1 percent followed >6 months). Clinical infection occurred in 121 patients (14.4 percent) with median time to infection of 22 days (95 percent CI 14-31). Overall 71.9 percent (87/121) of infected patients developed infection within 60 days of the date MRSA colonization was detected. However, 17/121 patients (14.0 percent) developed clinical infection more than six months after documented MRSA acquisition. The most common sites of clinical infection were skin and soft tissue (49/121, 40.5 percent, 95 percent CI 31.7-49.8), respiratory tract (37/121, 30.6 percent, 95 percent CI 22.5-39.6) and bone and joint infections (14/121, 11.6 percent, 95 percent CI 6.5-18.7). Thirteen patients (13/121, 10.7 percent, 95 percent CI 5.8-17.7) had bacteremias, of which six (5.0 percent 95 percent CI 1.8-10.5) were primary and seven (5.7 percent, 95 percent CI 2.3-11.6) were secondary to infection at other sites. Crude mortality at 30 days and six months was higher in patients with MRSA infection than colonization alone (aOR 5.49, 95 percent CI 2.75-10.95, p<0.001 and aOR 2.94, 95 percent CI 1.78-4.85, p<0.001 respectively).
The researchers concluded that risk of clinical infection is highest soon after MRSA acquisition and say that prevention of MRSA acquisition in the hospital will have significant impact on morbidity and mortality for patients. Their research was published in BMC Infectious Diseases.
Reference: Balm MND, Lover AA, Salmon S, Tambyah PA and Fisher DA. Progression from new methicillin-resistant Staphylococcus aureus colonization to infection: an observational study in a hospital cohort. BMC Infectious Diseases 2013, 13:491 doi:10.1186/1471-2334-13-491