Microbiological aspects and clinical impact of lower lung field TB in Peru

Who

• Participants: Individuals aged ≥14 years with newly diagnosed, microbiologically confirmed pulmonary tuberculosis (PTB).

• Sample size: 1,316 patients with abnormal baseline chest X-rays (CXRs); 84 (6%) had lower lung field (LLF) TB and 1,232 (94%) had non-LLF TB.

• Key characteristics: LLF TB patients were more likely to be women, have BMI >25 kg/m², be sputum smear–negative, have lower baseline St. George’s Respiratory Questionnaire (SGRQ) scores, and be infected with Mycobacterium tuberculosis (MTB) Lineage 2.

What

• Focus: The association between microbiological characteristics (sputum smear and culture status, MTB lineage) and radiographic localization of TB (LLF vs non-LLF), and the impact of LLF disease on treatment response and outcomes.

• Main findings:

  • LLF TB was independently associated with sputum smear negativity and infection with MTB Lineage 2.

  • Patients with LLF TB showed significantly less improvement in SGRQ scores after 2 months of treatment compared with non-LLF TB patients.

  • Final treatment outcomes appeared better in LLF TB but were not statistically significant after adjustment.

• Implications: LLF TB may be underdiagnosed using conventional sputum-based tests and is associated with slower early clinical improvement, suggesting a risk of ongoing transmission and the need for improved diagnostic strategies.

When

• Study period: October 2020 to December 2022.

Where

• Setting: Primary care health centers across 16 districts in Lima, Peru, including urban, peri-urban, and informal shantytown areas.

Why

• Rationale: Lower lung field TB can be difficult to detect with routine diagnostic approaches and may differ biologically and clinically from typical upper-lung TB. The study aimed to clarify microbiological correlates of LLF TB and assess whether LLF localization affects treatment response and outcomes.

How

• Design: Prospective cohort study.

• Diagnostics: Microbiological confirmation by GeneXpert MTB/RIF and/or sputum culture; drug susceptibility testing per WHO definitions.

• Radiography: Baseline and 2-month posteroanterior CXRs classified as LLF or non-LLF TB by radiologists.

• Molecular methods: Whole-genome sequencing of culture-positive isolates; MTB lineage determined using a 62-SNP barcode.

• Outcomes: Treatment response assessed by change in SGRQ score from baseline to 2 months; end-of-treatment outcomes classified by WHO criteria.

• Analysis: Multivariable regression adjusting for demographic and clinical covariates.

Source: Tan, Q., Huang, C.C., Calderon, R., Lecca, L., Mendoza, M., Rocha, G.R., Tintaya, K., Tovar, X., Feng, J.Y., Pan, S.W. and Tseng, Y.H., 2025. Microbiological aspects and clinical impact of lower lung field tuberculosis: An observational cohort study in Peru. International Journal of Infectious Diseases, 150, p.107284.