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Pulmonary Tuberculosis Infectiousness of Persons Identified Through Active and Passive Case-finding in a High-burden
Lilian N Njagi1, Khai Hoan Tram2, Jerry S Zifodya3
1Centre for Respiratory Diseases Research, Kenya Medical Research Institute, Nairobi, Kenya.
Background:
The role of active case-finding (ACF) in improving tuberculosis (TB) prevention and care depends on the infectiousness of persons with undiagnosed TB and the accuracy of screening strategies. To compare undiagnosed community dwellers to persons presenting for healthcare, we evaluated clinicodemographic and microbiologic characteristics, cough aerosol culture (CAC) status, and household contact (HHC) QuantiFERON-Plus (QFT) status by case-finding approach in adults with pulmonary TB.
Methods:
We enrolled 388 Kenyan adults with GeneXpert (excluding trace) and/or culture-confirmed, untreated TB through healthcare presentation (passive case-finding [PCF]; 87%) or ACF (community-based prevalence survey). Interventions included cough aerosol sampling and HHC QFT testing. We performed mixed-effect logistic regression to predict transmission, clustered on index participants.
Results:
World Health Organization-recommended screening symptoms (W4SS) were more common in the PCF cohort (99% vs 73%, P < .001). Traditional makers of infectiousness were less frequent in the ACF cohort. Higher symptom burden (number of reported World Health Organization-recommended 4-symptom screen) associated with higher bacillary burden (lower GeneXpert Ct) (estimate -0.55; 95% confidence interval [CI], -.98 to -.13; P = .01). Among 263 participants with CAC, 21% were CAC-positive, none of whom enrolled through ACF. Among 270 HHCs, QFT positivity differed by index CAC status (89% vs 56% in HHCs of CAC-positive and negative participants, respectively; P < .001) but not by traditional infectiousness makers or case-finding approach. Index CAC-positive status (adjusted odds ratio [aOR], 11.2; CI, 2.2-58.3), HIV-positive status (aOR, 0.1; CI, .0-.6), and HHCs age (aOR, 1.04; CI, 1.01-1.08), independently predicted HHC QFT positivity.
Conclusions:
Our findings suggest that ACF may detect a smaller proportion of CAC-positive persons with TB than PCF.
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