Abstract
BackgroundThere is a lack of recent studies examining recording of influenza-like illness (ILI) in primary care in the UK over time and according to population characteristics. Our aim was to determine time trends and socio-demographic patterns of ILI recorded consultations in primary care.MethodsWe used The Health Improvement Network (THIN) UK primary care database and extracted data on all ILI consultations between 1995 and 2013. We estimated ILI recorded consultation rates per 100,000 person-weeks (pw) by age, gender, deprivation and winter season. Negative binomial regression models were used to examine time trends and the effect of socio-demographic characteristics. Trends in ILI recorded consultations were compared to trends in consultations with less specific symptoms (cough or fever) recorded.ResultsThe study involved 7,682,908 individuals in 542 general practices. The ILI consultation rate decreased from 32.5/100,000 pw (95% confidence interval (CI) 32.1, 32.9) in 1995–98 to 15.5/100,000 pw (95% CI 15.4, 15.7) by 2010–13. The decrease occurred prior to 2002/3, and rates have remained largely stable since then. Declines were evident in all age groups. In comparison, cough or fever consultation rates increased from 169.4/100,000 pw (95% CI 168.6, 170.3) in 1995–98 to 237.7/100,000 pw (95% CI 237.2, 238.2) in 2010–13. ILI consultation rates were highest among individuals aged 15–44 years, higher in women than men, and in individuals from deprived areas.ConclusionThere is substantial variation in ILI recorded consultations over time and by population socio-demographic characteristics, most likely reflecting changing recording behaviour by GPs. These results highlight the difficulties in using coded information from electronic primary care records to measure the severity of influenza epidemics across time and assess the relative burden of ILI in different population subgroups.
Highlights
The influenza virus is a common cause of respiratory tract infections
The influenza-like illness (ILI) consultation rate decreased from 32.5/100,000 pw (95% confidence interval (CI) 32.1, 32.9) in 1995–98 to 15.5/100,000 pw by 2010–13
Cough or fever consultation rates increased from 169.4/100,000 pw in 1995–98 to 237.7/100,000 pw in 2010–13
Summary
The influenza virus is a common cause of respiratory tract infections. Antigenic shift of the virus may lead to pandemics,[1] the most recent caused by influenza A/H1N1 in 2009.[2]. Primary care surveillance is based on a clinical diagnosis of influenza-like illness (ILI), rather than influenza itself. The symptoms included in the clinical definition of ILI include sudden onset of fever (above 38.5°C) and cough.[7, 8] ILI symptoms can be caused by a number of other viruses, including adenovirus, rhinovirus and human metapneumovirus.[9, 10] persons with influenza may not receive a diagnosis of ILI when they consult primary care. A recent community study demonstrated that only 8% of a small sample of symptomatic individuals with confirmed influenza who consulted their GP had ILI recorded in their primary care record.[11]. There is a lack of recent studies examining recording of influenza-like illness (ILI) in primary care in the UK over time and according to population characteristics.
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