Rationing tests for drug-resistant tuberculosis - who are we prepared to miss?

Area of Science:

• Public Health
• Infectious Diseases
• Clinical Diagnostics

Background:

• Early identification of drug-resistant tuberculosis (DR-TB) is vital for treatment success and preventing transmission.
• Resource-limited settings often ration drug susceptibility testing (DST) using risk profiling.
• Previous studies have not quantified the number of DR-TB cases missed by this rationing strategy.

Purpose of the Study:

• To quantify the proportion of patients with DR-TB missed when DST is rationed based on multidrug-resistant TB (MDR-TB) risk factors.
• To evaluate the impact of risk-based rationing on the number of DSTs needed and the proportion of missed DR-TB cases.
• To inform diagnostic strategies in settings with ongoing DR-TB transmission.

Main Methods:

• A cohort of 1,545 individuals with suspected TB symptoms in Lima, Peru, provided sputum for TB culture and DST.
• Clinic-epidemiological questionnaires identified patients with MDR-TB risk factors.
• Data were analyzed to calculate the proportion of drug resistance and the effect of rationing DST.

Main Results:

• Culture-positive TB was found in 9.5% of subjects, with 21.8% of these cases being DR-TB.
• Of 553 subjects with MDR-TB risk factors, only 2.7% had DR-TB, while 53.2% of all DR-TB cases were missed when DST was rationed.
• Rationing DST to individuals with risk factors would miss more than half (53.2%) of the DR-TB population.

Conclusions:

• Rationing DST based on known MDR-TB risk factors results in an unacceptable proportion of missed DR-TB cases.
• This strategy is particularly detrimental in settings with ongoing DR-TB transmission.
• Investment in universal DST for all presumptive TB cases should be prioritized to improve patient outcomes and control transmission.