"National Danish Case-control Study of Community Onset Infections Caused by MRSA: Presented at ECCMID"
By Chris Berrie
NICE, FRANCE -- April 6, 2006 -- The alarming increase of methicillin-resistant Staphylococcus aureus (MRSA) cases in Denmark is closely related to skin and soft tissue infections where there is a high prevalence of underlying skin disease and independent risk factors involved are foreign ethnicity and prior hospitalisation.
Sidsel Böcher, MD, project manager and PhD student, Staphylococcus Laboratory, National Centre for Antimicrobials and Infection Control, Copenhagen, Denmark, reported on this multicentre, prospective, case-control study here April 3[rd at the 16th European Congress of Clinical Microbiology and Infectious Diseases on behalf of the Danish CA-MRSA Study Group. Mr. Böcher conducted his research with Robert Skov, MD, head of the Staphylococcus Laboratory.
Along with other Scandinavian countries, Denmark has remained a low prevalence area for MRSA, with <1% MRSA found in bacteremias up to 2005. However, the last 3 to 4 years have seen more or less a doubling of the number of MRSA cases each year, which appears to be driven by cases of community-acquired infection (CA-MRSA).
To characterise and identify the risk factors for CA-MRSA infections in this still-low-prevalence country, Mr. Böcher and colleagues looked at infections in 2004 in the population of Denmark (5.4 million).
Cases were defined as patients infected with culture-confirmed MRSA who presented to a general practitioner (GP), a hospital outpatient clinic or a skin clinic. Control patients were similarly defined, with infection being for methicillin-sensitive Staphylococcus aureus (MSSA).
Data were collected by interview and questionnaire that included patient demographics, previous exposure to infection and clinical details. The design was for a weighed randomisation of cases to controls of 1:3, with a sample size of 200 cases. However, some statistical power was lost due because only 1 in 3 potential cases agreeing to participate, and to some organisational difficulties, Mr. Böcher.
The demographic status of the patients from the MRSA (n = 34; median age, 38 years; male/female, 1.0) and MSSA (n = 87; median age, 43 years; male/female, 0.7) groups showed equivalent socio-economic status, but different household sizes (1-3 vs. 1-6 people, respectively) and countries of origin. For the last of these, while the MSSA controls were more or less all Danish in origin (except one half Swedish), those in the MRSA group were 76% Danish, with USA (2 cases), Jordan (2), Spain (1), Switzerland (1), Finland (1) and Ireland (1) also represented.
Univariate analysis of the range of risk/exposure factors considered only showed a significant difference across the two groups for this foreign ethnicity (MRSA, 24%; MSSA, 1%; P <.01). When taken to the multivariate level as a consideration of the independent risk factors for CA-MRSA infections in Denmark, foreign ethnicity again proved significant (odds ratio [OR], 30.5; 95% confidence interval [CI], 3.6-257.3) while hospitalisation (<6 months, >7 days; OR, 5.7; 95% CI, 0.90-36.4) showed a trend that was close to significance.
An analysis of the clinical data indicated that skin and soft tissue infections (face, legs, hands) predominated (MRSA, 68%; MSSA, 60%), with underlying skin disease seen in 27% and 38% of the patients, respectively. Other underlying illnesses included asthma/cold (8%, 11%) and diabetes (5%, 9%).
The researchers also carried out an analysis of the distribution of clonal complexes on the MRSA group. The main MRSA clones were CC80, CC5, CC8, CC30 and CC45. The relative distributions of all the MRSA clones seen also closely followed a previous analysis of all of the 255 CA-MRSA patients in Denmark in 2004, thus confirming the community-acquired nature of the present cases.
Although limited by the lower than planned number of cases, this study does indicate that CA-MRSA patients tend to show skin and soft tissue infections, with a high prevalence of underlying skin disease. Furthermore, the majority had received antibiotics within the previous 6 months, and they showed a relatively high hospitalisation rate.
As indicated above, the only independent risk factor was foreign ethnicity, with prior recent hospitalisation tending towards a risk factor.
"So our recommendation to physicians is that they should have these results in mind when deciding about empiric treatment of suspected S. aureus infection," Mr. Böcher concluded.
[Presentation title: National Danish Case-control Study of Community Onset Infections Caused by MRSA. Abstract O313]
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