P161 Blood neutrophil count at 1 month of treatment predicts the radiological severity of post-tuberculous lung disease

Background Post-tuberculous lung disease contributes to morbidity in pulmonary tuberculosis (PTB) survivors. However, the determinants of persistent lung damage are not well established and may relate to socio-demographic factors, bacterial burden, delayed presentation to healthcare or host immune responses (especially neutrophils, implicated in bronchiectasis pathogenesis and cavitation). We investigated associations between radiological post-tuberculous lung disease and these potential predictors. Methods We collected data from patients treated for PTB at our centre over a 5.5 year period excluding those with HIV infection, other known immunodeficiencies or immunosuppressive medication, pre-existing structural lung disease, drug resistant infection or with disease sites not including lungs or pleura. We recorded age, sex, ethnicity, smoking status, duration of symptoms, sputum smear acid fast bacilli grade, time to culture positivity and blood results (C-reactive protein and neutrophil count) at baseline and at 1 month. Chest x-rays performed at baseline, 2 months and end of treatment (at a median of 195 days from treatment initiation) were assessed by two radiologists independently and scored using a validated system. Relationships between predictor variables and radiological outcomes were assessed using linear or binary logistic regression as appropriate. Results We assessed 156 individuals, mean age 37 years, 62% male. Baseline and 2-month radiological severity correlated with age, ethnicity (higher scores in white patients), grade of sputum smear positivity and blood inflammatory markers and inversely with time to culture positivity. In multivariate analysis only sputum smear grade (pl0.001) and neutrophil count (p=0.001) retained significance. At end of treatment, only the 1-month neutrophil count (not baseline neutrophil count) was significantly associated with overall radiological severity (r=0.32, p=0.005) in multivariate analysis. The 1-month neutrophil count was also the only independent correlate of volume loss (odds ratio (OR)=1.25 per 1 × 109 increase in neutrophils, p=0.04) and pleural thickening (OR=1.23, p=0.04). 1-month neutrophil counts were higher in patients with persistent cavitation or effusion at end of treatment compared to those without. Conclusions Persistent neutrophilic inflammation after 1 month of anti- tuberculosis therapy is associated with poor radiological outcome, suggesting both a target for interventions to minimise post-tuberculous lung disease and a means to identify people at greatest risk.