Influenza-attributable burden in United Kingdom primary care

Abstract

Influenza is rarely laboratory-confirmed and the outpatient influenza burden is rarely studied due to a lack of suitable data. We used the Clinical Practice Research Datalink (CPRD) and surveillance data from Public Health England in a linear regression model to assess the number of persons consulting UK general practitioners (GP episodes) for respiratory illness, otitis media and antibiotic prescriptions attributable to influenza during 14 seasons, 1995-2009. In CPRD we ascertained influenza vaccination status in each season and risk status (conditions associated with severe influenza outcomes). Seasonal mean estimates of influenza-attributable GP episodes in the UK were 857 996 for respiratory disease including 68 777 for otitis media, with wide inter-seasonal variability. In an average season, 2·4%/0·5% of children aged <5 years and 1·3%/0·1% of seniors aged ⩾75 years had a GP episode for respiratory illness attributed to influenza A/B. Two-thirds of influenza-attributable GP episodes were estimated to result in prescription of antibiotics. These estimates are substantially greater than those derived from clinically reported influenza-like illness in surveillance programmes. Because health service costs of influenza are largely borne in general practice, these are important findings for cost-benefit assessment of influenza vaccination programmes.

Trial registration: ClinicalTrials.gov NCT01520935.

Keywords: Epidemiology; GP surveillance systems; infectious disease; influenza; influenza vaccines.

Fig. 1.

Attribution modelling showing excess GP episodes attributable to influenza A and B and respiratory syncytial virus (RSV) in children aged 5–17 years. The pattern was observed to be the same for other age groups. ‘All other’ refers to GP episodes not attributable to influenza or RSV. The denominator is the UK population.

Fig. 2.

Seasonal rates (with 95% confidence intervals) of GP episodes for respiratory disease (broadly defined) attributable to influenza A, influenza B and respiratory syncytial virus (RSV).

Fig. 3.

The percentage of the estimated burdens for several outcomes attributed to influenza A and influenza B by five age groups (mean across seasons). The total number of GP episodes for each outcome was: respiratory disease (broadly defined) (n = 857 996), bronchitis and bronchiolitis (n = 248 727), influenza-like illness (n = 265 123), pneumonia and influenza (n = 197 769), otitis media (n = 68 777), antibiotic use (n = 604 042).