The contribution of respiratory pathogens to the seasonality of NHS Direct calls

Abstract

Objectives: Primary care is thought to bear half the cost of treating infections in the UK. We describe the seasonal variation in NHS Direct respiratory calls (a new source of primary care data) and estimate the contribution of specific respiratory pathogens to this variation.

Methods: Linear regression models were used to estimate the weekly contribution of specific respiratory pathogens to the volume of NHS Direct respiratory calls (England and Wales, 2002-2004, all ages and 0-4 years).

Results: Annual peaks in NHS Direct cough and difficulty breathing calls occurred in late December, with peaks in 'cold/flu' and fever calls occurring between November and April. The main explanatory variables were influenza (estimated to account for 72.5 calls per 100,000/year; 22% of 'cold/flu' calls; 15% of cough; and 13% of fever) and Streptococcus pneumoniae (55.5 per 100,000; 33% of 'cold/flu' calls; 20% of cough; and 15% of fever (0-4 years)).

Conclusions: It is estimated that respiratory viruses, notably influenza and RSV, are responsible for at least 50% of the seasonal variation in NHS Direct respiratory calls. These results provide estimates of the burden of specific respiratory diseases reported to NHS Direct, and will help interpret syndromic surveillance data used to provide early warning of rises in community morbidity.

Figure 1

Weekly variation in laboratory reports of respiratory pathogens (October 2002–October 2004), displayed as a proportion of total reports for each pathogen. (Pathogens that significantly influenced the models are colour coded; pathogens with <100 reports per year are not displayed).

Figure 2

Comparison of the observed number of NHS Direct ‘cold/flu’ calls (all ages) with the estimated numbers due to influenza, Streptococcus pneumoniae, rhinovirus and other causes (October 2002–October 2004) (model CF1).

Figure 3

(a) Comparison of the observed number of NHS Direct cough calls (all ages) with the estimated numbers due to influenza, RSV, Streptococcus pneumoniae, rhinovirus, bank holidays and other causes (October 2002–October 2004) (model C1). (b) Comparison of the observed number of NHS Direct cough calls (0–4 years) with the estimated numbers due to influenza, RSV, Mycoplasma pneumoniae, rhinovirus, parainfluenza, bank holidays and other causes (October 2002–October 2004) (model C1 (0–4 years)).

Figure 4

Comparison of the observed number of NHS Direct fever calls (0–4 years) with the estimated numbers due to influenza, Streptococcus pneumoniae and other causes (October 2002–October 2004) (model F1).