Investigation into early mortality in Malawian adults treated for pulmonary tuberculosis

CJ Waitt1,2, NPK Banda2,3, SA White2, B Kampmann5, J Kumwenda2, RS Heyderman2,4, M Pirmohamed1, SB Squire4. 1University of Liverpool, Liverpool, UK, 2Malawi-Liverpool-Wellcome Trust Clinical Research Programme, Blantyre, Malawi, 3Department of Medicine, College of Medicine, Blantyre, Malawi, 4Liverpool School of Tropical Medicine, Liverpool, UK, 5Imperial College London, London, UK

Background and Aims: Tuberculosis is among the most common causes of death worldwide, and despite the availability of effective chemotherapeutic agents, a death rate of up to 20% was described in Malawi in the decade between 1995 and 2005. Review of existing studies seeking to determine causes and risk factors for death during TB revealed a dearth of prospective clinical studies [1]. We therefore aimed to evaluate clinical and immunological risk factors for death and clinical deterioration (poor outcome) during the intensive phase of TB treatment in Malawi.

Methods and Results: Analysis of 199 patients with microbiologically confirmed pulmonary TB demonstrated that major causes of poor outcome were progression of tuberculosis itself, or a presumed superadded non-tuberculosis infection. With appropriate, often simple, treatment, the majority of patients presenting with superadded infection recovered and completed TB treatment uneventfully. There was no statistically significant difference in the frequency of poor outcome between HIV positives and negatives. Multivariate logistic regression analysis of potential risk factors demonstrated that a combination of elevated respiratory rate and reduced BMI identified high risk patients with 72% sensitivity and 71% specificity. These findings need to be validated in a larger cohort [2].

It was hypothesised that patients suffering clinical deterioration would mount an exaggerated pro-inflammatory response to mycobacterial antigens. However, using a whole blood assay, patients with poor outcome produced significantly lower levels of the pro-inflammatory cytokine TNFα in response to stimulation with Mycobacterium tuberculosis H37Rv (p=0.041) and lipopolysaccharide (p=0.017) [2].

Using a 17-plex panel, serum and antigen-induced cytokine responses were compared in the 22 patients who died or deteriorated compared with HIV, CD4 count and sex-matched controls who had an uneventful clinical course. In addition to TNFα (p=0.01), there was lower production of IL1β (p=0.006) and IL7 (p=0.009) in response to stimulation; these perturbations resolved with successful TB treatment, suggesting that this dysregulation is a consequence of tuberculosis rather than intrinsic to the host.

Intracellular cytokine staining demonstrated the major TNFα producing cell to be the ‘classical’ CD14hiCD16neg monocyte with lower production from CD14loCD16hi cells (p<0.0001). Reduced TNFα production in response to H37Rv and LPS was paralleled by reduced responses to purified toll like receptor (TLR) ligands, suggesting a generalised dysfunction in the TLR signalling pathways. Further work exploring the role of TLR polymorphisms would be informative. To determine whether the monocyte hyporesponsiveness seen in this population was analogous to that described in sepsis, HLA-DR, CD86, TLR2, TLR4 and CD16 expression were measured longitudinally. No correlation existed between these values and TNFα production. This suggests the mechanism of reduced TNFα in this population of TB patients does not parallel that reported in sepsis.

Conclusion: These studies have provided novel insight into the causes, risk factors and mechanisms of clinical deterioration and death in Malawian TB patients during the intensive phase of treatment.

1) Waitt, C.J. and S.B. Squire Int J Tuberc Lung Dis, 2011. 15(7): p. 871-85.

2) Waitt, C.J., et al. J Infect Dis, 2011. 204(3): p. 358-62.