‘Robust association’ between GP antibacterial prescriptions and MRSA in children

GP prescribing of antibacterial drugs can raise the risk of MRSA infections in children and adolescents, UK data shows.

A study by Canadian researchers, looking at data held in the UK General Practice Research Database, showed prior prescribing of antibacterial drugs in the community is associated with an increased dose-dependent risk of MRSA.

GP prescribing of antibacterial drugs between 30 and 180 days prior to the index data was associated with a 3.5-fold increased risk of an MRSA infection compared with age- and practice-matched controls.

The researchers identified all children in the database aged one to 19 between 1994 and 2007, and their exposure to antibacterial drugs in the 180 to 30 days prior to the date a Read code was entered for a community-associated MRSA infection. All patients were matched with controls and the data adjusted for co-morbidities, other prescription drug use and hospitalisation.

The average annual incidence of MRSA was 4.5 per 100,000 children per year, for children of all ages. The analysis was narrowed to include only children with more than one year of follow-up data. Of the 97 cases and 9,357 controls, 52.5% and 13.6% received antibacterial drug prescriptions during the 150-day exposure window, respectively.

The adjusted relative risk of an MRSA diagnosis was 3.5-times higher in children prescribed any antibacterial drug compared with controls.

 The relative risk of a diagnosis increased with the number of prescriptions, to 2.2, 3.3, 11.0, and 18.2 children prescribed one, two, three and four prescriptions, respectively. The relative risk was highest for quinolones, at 14.8 (see table below).

The researchers argued said they could not prove the association was causal, but argued ‘the association was not only dose and class dependent but also responsive to modifying the length of the exposure time window, which implies time dependency' – supporting causality.

Dr Verena Schneider-Lindner, a researcher in epidemiology and biostatistics at McGill University in Montreal, concluded: ‘While close to half of children were diagnosed as having MRSA in the community without prior antibacterial drugs, such agents are associated-with a dose-dependent increased risk, concordant with findings in adults.'

‘In conclusion, antibacterial agents are not a necessary precondition for MRSA, but there is a robust association of antibacterial drug prescriptions with a subsequent diagnosis of MRSA for children in the community.'

Professor Chris Butler, professor of primary care medicine at the University of Cardiff and a GP in the city, said: ‘We don't want to generate an unhelpful fear of antibiotics treatment in people's minds, but we should be doing more to limit antibiotics to only those who are likely to benefit. Antibiotics upset the microbiological ecology in individuals, putting them at some risk of future harm from resistant infections.'

Professor Paul Little, professor of primary care research at the University of Southampton and a GP in Salisbury, said: ‘The authors performed their analyses in a comprehensive way and the findings suggest yet another reason to be cautious about antibiotic prescribing, and that there is reason to be particularly careful with macrolides and quinolones.'

Risk of MRSA infection with different antibacterials

Source: Arch Pediatr Adolesc Med 2011, published online August 1