Mycobacterium tuberculosis transmission from tuberculosis patients with and without recognized symptoms: a case-contact study in eastern China

A large number of tuberculosis patients manifest with minimal or no symptoms, and the infectiousness of these individuals is not well characterized. Index cases were consecutively enrolled from the four health centers in Jiangsu Province. Symptoms among index cases were assessed covering the 3 months prior to diagnostic evaluation, in addition to those present at the time of diagnosis. Concurrently, one control community was selected for QuantiFERON screening. Mycobacterium tuberculosis infection was measured through QuantiFERON for all groups. 1,050 contacts of 473 tuberculosis patients, and 560 unexposed controls were included. Asymptomatic tuberculosis among index cases varied from 15% (no symptoms), to 24% (no cough), and 44% (no prolonged cough). The relative risk of QuantiFERON positivity was higher than controls compared to contacts of both asymptomatic (aRR; 2.06; 1.28-3.33) and symptomatic tuberculosis patients (aRR; 2.23; 1.66-3.01). When using alternative QuantiFERON cutoffs, the relative risk was consistently higher among both contact groups compared to controls. When comparing contacts of symptomatic and asymptomatic tuberculosis patients, similar rates of QuantiFERON and ESAT6-CFP10 skin test levels were seen, regardless of the cutoff. This study suggests that tuberculosis patients that are minimally symptomatic or without recognized symptoms may be infectious.