Two analyses using data extracted from the UK Clinical Practice Research Datalink (CPRD) are reported: a retrospective longitudinal analysis of MC cases presenting to general practice in the UK, and an age–sex matched case-cohort analysis to examine the likelihood of developing MC in children who have previously presented to general practices with AE. MC and AE were defined as having a Read Code for either condition (information available from authors on request) if aged 0–14 years at the time of consultation between 2004 and 2013 (inclusive). Controls for the case-cohort analysis were selected at random within age–sex strata at a ratio of 1:1. Patients were excluded from the population pool before the controls were selected if they had a Read Code of AE, ‘transferred out of practice’, or if they died during the study period. All data were extracted from the CPRD, which is a primary care database of anonymised patient records, representing approximately 6% of the UK population. CPRD contains data on >4 million active patients from >500 primary care practices across the UK.16 The base population for both analyses was all CPRD-registered patients aged 0–14 years per year for the period 2004–2013. Patients must have been registered in the practice during the year to be included within the denominator population for that year. Only data from GP practices that were defined as ‘up to standard’ by the CPRD standard definition were included within the study. The data extraction process is shown in Figure 1.
How this fits in
Molluscum contagiosum (MC) is a common skin condition in children but recent consultation rates have not been described in the UK. It is common that children with MC also present with atopic eczema (AE) to primary and secondary care; however, the risk of developing MC in children with a history of AE is not clear. The largest rate of consultations of MC was found in children aged 1–4 years and 5–9 years (13.1 to 13.0 [males] and 13.0 to 13.9 [females] per 1000 respectively), and consultation rates have decreased from 2004 to 2013 by 50% for MC. Evidence was found of an increased likelihood of subsequent MC in children with a primary care diagnosis of AE.