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Abstract
Introduction and objectives The incidence of empyema has been increasing in children. We investigated trends in the incidence of empyema cases over the time period 2006–2010 in relation to temperature, rainfall and the introduction of the pneumococcal vaccine using regression analysis.
Methods All admissions with ICD-10 codes J86.0 and J86.9 coding for pyothorax with/without fistula from 1st January 2006 until 31st May 2010 were collated. A generalised least squares (GLS) modelling technique was employed to investigate trends in child cases in relation to local average monthly maximum temperature and monthly rainfall. The timing of the introduction of the PCV-7 vaccine was included as a co-variate.
Results 183 cases of paediatric empyema were identified. There was a negative relationship between number of cases of childhood empyema and average maximum temperature in the month of admission (t=−2.24, p>0.00). Introduction of the PCV-7 vaccine was associated with a reduction in cases (t=−5.00, p=0.02). There was no significant relationship between the number of cases and average monthly rainfall. There was no significant evidence of autocorrelation for this model suggesting that the number of cases each month were independent of the number in the preceding or following month. Fitted values from the model and the observed trend in cases are shown in Abstract P81 Figure 1. The number of cases appears to be inversely related to temperature variation across the year. The R-squared of the final model was 0.36, whilst the R-squared for model without the vaccine was 0.30, suggesting that 6 % of the variation in cases could be explained by the introduction of the vaccine.
Conclusions Mean maximum temperature in the month of admission appears to be a significant predictor of cases of empyema and correlates with the cyclical pattern of cases. Introduction of PCV-7 vaccine was associated with a reduction in the number of cases which may be related to a combination of direct and indirect vaccine effects secondary to improved herd immunity. Further work is required to establish whether this finding is generic across the UK and the underlying mechanisms driving this phenomenon.
Variation in monthly admissions of children with empyema and variation in mean monthly maximum temperature from January 2006—May 2010. 1st plot: Grey line—observed number of admissions, Black line—admissions predicted by model.