Sociodemographic and geospatial associations with community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections in a large Canadian city: an 11 year retrospective study

Abstract

Background: The first Canadian outbreak of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) was identified in 2004 in Calgary, Alberta. Using a novel model of MRSA population-based surveillance, sociodemographic risk associations, yearly geospatial dissemination and prevalence of CA-MRSA infections over an 11 year period was identified in an urban healthcare jurisdiction of Calgary.

Methods: Positive MRSA case records, patient demographics and laboratory data were obtained from a centralized Laboratory Information System of Calgary Laboratory Services in Calgary, Alberta, Canada between 2004 and 2014. Public census data was obtained from Statistics Canada, which was used to match with laboratory data and mapped using Geographic Information Systems.

Results: During the study period, 52.5% of positive MRSA infections in Calgary were CA-MRSA cases. The majority were CMRSA10 (USA300) clones (94.1%; n = 4255), while the remaining case (n = 266) were CMRSA7 (USA400) clones. Period prevalence of CMRSA10 increased from 3.6 cases/100000 population in 2004, to 41.3 cases/100000 population in 2014. Geospatial analysis demonstrated wide dissemination of CMRSA10 annually in the city. Those who are English speaking (RR = 0.05, p < 0.0001), identify as visible minority Chinese (RR = 0.09, p = 0.0023) or visible minority South Asian (RR = 0.25, p = 0.015), and have a high median household income (RR = 0.27, p < 0.0001) have a significantly decreased relative risk of CMRSA10 infections.

Conclusions: CMRSA10 prevalence increased between 2004 and 2007, followed by a stabilization of cases by 2014. Certain sociodemographic factors were protective from CMRSA10 infections. The model of MRSA population-surveillance and geomap outbreak events can be used to track the epidemiology of MRSA in any jurisdiction.

Keywords: CA-MRSA; CMRSA10; Geospatial analysis; Laboratory medicine.

Fig. 1

Flow diagram of inclusion (left) and exclusion (right) criteria of study population (2004–2014)

Fig. 2

Geospatial dissemination of CMRSA10 cases in Calgary, Alberta during select years of the study period. In 2004 (top left), small clusters of CMRSA10 infections in the city of Calgary were already widely disseminated across the city, including the downtown city centre (just south of the Bow River that passes through the city from west to east) and the northern half of the city. Two clusters of up to 3 cases were located both in downtown and the southwest quadrant of the city. In 2005 (top right), the number of cases rapidly increased, spreading in the communities along the Bow River, extending further east and to the southern part of the city. Cases continued to spread and disseminate outwards in all directions as prevalence of CMRSA10 increased in 2007 (bottom left). The downtown core and just east of the Bow River visually appear to be focal regions for CMRSA10 cases, with multiple regions of up to 26 cases per cluster. In 2014 (bottom right), there appeared to be a relative stabilization of positive cases since 2007. For a video of CMRSA10 spread throughout Calgary annually between 2004 and 2014, please see Additional file 1