title: Recording of Influenza-Like Illness in UK Primary Care 1995-2013: Cohort Study.
abstract: BACKGROUND
  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. Our aim was to determine time trends and socio-demographic patterns of ILI recorded consultations in primary care.
  
  
  METHODS
  We 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.
  
  
  RESULTS
  The 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.
  
  
  CONCLUSIONS
  There 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.
authors.affiliation: Population, Policy and Practice Programme, University College London Institute of Child Health, London, United Kingdom; Research Department of Primary Care and Population Health, University College London, London, United Kingdom.
authors.forename: Pia
authors.initials: P
authors.lastname: Hardelid
authors.affiliation: PRIMENT Clinical Trials Unit, Research Department of Primary Care and Population Health, University College London, London, United Kingdom.
authors.forename: Greta
authors.initials: G
authors.lastname: Rait
authors.affiliation: Population, Policy and Practice Programme, University College London Institute of Child Health, London, United Kingdom.
authors.forename: Ruth
authors.initials: R
authors.lastname: Gilbert
authors.affiliation: Research Department of Primary Care and Population Health, University College London, London, United Kingdom; Department of Clinical Epidemiology, Aarhus University, Aarhus, Denmark.
authors.forename: Irene
authors.initials: I
authors.lastname: Petersen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003371:Cough / Q000175:diagnosis / Q000453:epidemiology; D016208:Databases, Factual / Q000706:statistics & numerical data*; D058872:Epidemics; D005260:Female; D005334:Fever / Q000175:diagnosis / Q000453:epidemiology; D058006:General Practice / Q000706:statistics & numerical data*; D006801:Humans; D007223:Infant; D007251:Influenza, Human / Q000175:diagnosis* / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D011320:Primary Health Care / Q000706:statistics & numerical data*; D012044:Regression Analysis; D012621:Seasons; D012959:Socioeconomic Factors; D006113:United Kingdom / Q000453:epidemiology