Sputum-negative pulmonary tuberculosis in Shanghai, China: notification, clinical characteristics and outcomes.

backgroundWith the scaling up of WHO-recommended diagnostics, 40% of pulmonary tuberculosis (PTB) cases were still clinically diagnosed without sputum biological confirmation in China. To better understand this early paucibacillary disease, we explored notification, clinical characteristics and outcomes of sputum-negative PTB in Shanghai, China.

methodsWe accessed PTB surveillance data in Shanghai, China, from 2010 to 2019. All presumptive PTB patients underwent at least one sputum biological diagnostic (i.e., smear, culture, GeneXpert MTB/RIF). Any positive was defined as sputum-positive, otherwise sputum-negative. Data of newly diagnosed secondary PTB patients was extracted for analysis. The annual notification of sputum-negative PTB was calculated. Clinical characteristics and treatment outcomes were compared between sputum-negative and positive PTB. Missing data were addressed using multiple imputation. Log-binomial, logistic and Cox models were used to adjust potential confounders.

resultsOf 56,851 PTB patients in 2010-2019, 26,858 (47.2%) were sputum-negative. The annual notification declined from 12.2 per 100,000 in 2010 to 7.9 per 100,000 in 2019 (P for trend < 0.001). The median age of sputum-negative PTB patients was 35 (interquartile range 25, 55), with 34.1% of females, 50.7% of local residents. Compared to patients with sputum-positive PTB, sputum-negative PTB patients had a shorter delay in health seeking (10 vs. 12 days, Padj<0.001), but a longer delay in diagnosis (11 vs. 7 days, Padj<0.001). Besides, they had a higher proportion of detection through active screening (Padj<0.001), pleurisy (Padj<0.001), and a lower proportion of pulmonary cavities (Padj<0.001), diabetes (Padj<0.001), bronchial tuberculosis (Padj<0.001). 53,204 PTB patients were successfully treated (95.7% in sputum-negative vs. 91.7% in sputum-positive) and were followed for 368804.5 person-years. Compared to sputum-positive patients, sputum-negative PTB patients showed lower rates of treatment failure (0.2% vs. 0.6%, ORadj=0.56, 95%CI 0.52-0.61), death (1.4% vs. 3.9%, ORadj=0.43, 95%CI 0.38-0.49) and recurrence (2.1% vs. 3.3%, HRadj=0.71, 95%CI 0.63-0.79).

conclusionsAs a less severe disease, sputum-negative PTB had fewer comorbidities, radiological abnormalities, and better treatment outcomes, but a longer delay in diagnosis, which indicated the urgent need for novel biomarkers to enhance early detection of sputum-negative PTB.