BACKGROUND: Identifying and tackling the social determinants of infectious 
diseases has become a public health priority following the recognition that 
individuals with lower socioeconomic status are disproportionately affected by 
infectious diseases. In many parts of the world, epidemiologically and 
genotypically defined community-associated (CA) methicillin-resistant 
Staphylococcus aureus (MRSA) strains have emerged to become frequent causes of 
hospital infection. The aim of this study was to use spatial models with 
adjustment for area-level hospital attendance to determine the transmission 
niche of genotypically defined CA- and health-care-associated (HA)-MRSA strains 
across a diverse region of South East London and to explore a potential link 
between MRSA carriage and markers of social and material deprivation.
METHODS AND FINDINGS: This study involved spatial analysis of cross-sectional 
data linked with all MRSA isolates identified by three National Health Service 
(NHS) microbiology laboratories between 1 November 2011 and 29 February 2012. 
The cohort of hospital-based NHS microbiology diagnostic services serves 867,254 
usual residents in the Lambeth, Southwark, and Lewisham boroughs in South East 
London, United Kingdom (UK). Isolates were classified as HA- or CA-MRSA based on 
whole genome sequencing. All MRSA cases identified over 4 mo within the 
three-borough catchment area (n = 471) were mapped to small geographies and 
linked to area-level aggregated socioeconomic and demographic data. Disease 
mapping and ecological regression models were used to infer the most likely 
transmission niches for each MRSA genetic classification and to describe the 
spatial epidemiology of MRSA in relation to social determinants. Specifically, 
we aimed to identify demographic and socioeconomic population traits that 
explain cross-area extra variation in HA- and CA-MRSA relative risks following 
adjustment for hospital attendance data. We explored the potential for 
associations with the English Indices of Deprivation 2010 (including the Index 
of Multiple Deprivation and several deprivation domains and subdomains) and the 
2011 England and Wales census demographic and socioeconomic indicators 
(including numbers of households by deprivation dimension) and indicators of 
population health. Both CA-and HA-MRSA were associated with household 
deprivation (CA-MRSA relative risk [RR]: 1.72 [1.03-2.94]; HA-MRSA RR: 1.57 
[1.06-2.33]), which was correlated with hospital attendance (Pearson correlation 
coefficient [PCC] = 0.76). HA-MRSA was also associated with poor health (RR: 
1.10 [1.01-1.19]) and residence in communal care homes (RR: 1.24 [1.12-1.37]), 
whereas CA-MRSA was linked with household overcrowding (RR: 1.58 [1.04-2.41]) 
and wider barriers, which represent a combined score for household overcrowding, 
low income, and homelessness (RR: 1.76 [1.16-2.70]). CA-MRSA was also associated 
with recent immigration to the UK (RR: 1.77 [1.19-2.66]). For the area-level 
variation in RR for CA-MRSA, 28.67% was attributable to the spatial arrangement 
of target geographies, compared with only 0.09% for HA-MRSA. An advantage to our 
study is that it provided a representative sample of usual residents receiving 
care in the catchment areas. A limitation is that relationships apparent in 
aggregated data analyses cannot be assumed to operate at the individual level.
CONCLUSIONS: There was no evidence of community transmission of HA-MRSA strains, 
implying that HA-MRSA cases identified in the community originate from the 
hospital reservoir and are maintained by frequent attendance at health care 
facilities. In contrast, there was a high risk of CA-MRSA in deprived areas 
linked with overcrowding, homelessness, low income, and recent immigration to 
the UK, which was not explainable by health care exposure. Furthermore, areas 
adjacent to these deprived areas were themselves at greater risk of CA-MRSA, 
indicating community transmission of CA-MRSA. This ongoing community 
transmission could lead to CA-MRSA becoming the dominant strain types carried by 
patients admitted to hospital, particularly if successful hospital-based MRSA 
infection control programmes are maintained. These results suggest that 
community infection control programmes targeting transmission of CA-MRSA will be 
required to control MRSA in both the community and hospital. These 
epidemiological changes will also have implications for effectiveness of 
risk-factor-based hospital admission MRSA screening programmes.