Factors associated with variations in the rate of referrals and microbiology of pleural infection

Objectives: Invasive pneumococcal disease is seasonal and associated with influenza, but the same is uncertain for pleural infection. We set out to investigate whether pleural infection referrals similarly correlate with the seasonal variation in influenza burden and whether the microbiologic etiology varies according to certain factors. Methods: Cases of pleural infection were retrieved from the database of a Pleural Unit in a tertiary hospital in the UK. The rate of referrals for pleural infection was compared to contemporary national rates of influenza hospitalizations and primary care presentation with influenza like illnesses. Results: Between August 2015 and December 2019, 157 cases of pleural infection were diagnosed. The monthly rate of referrals with pleural infections was 3.8 cases/month, but this varied between months [range 0–6 cases]. No clear increase in pleural infection referrals coinciding or falling after peak influenza diagnosis was observed. However, the rate of infection referrals correlated positively with the overall monthly volume of pleural referrals (β 0.035, p = 0.004). Gram negative bacteria seemed more common during the hotter months, in hospital-acquired infections and in younger adults. Young adults were more commonly infected with pneumococci than older adults, who were more vulnerable to anaerobic infections. Conclusion: Direct association between the rate of pleural infection cases and influenza activity was not identified. Pleural infection microbiology appears to differ according to age and environmental temperatures.