Drug resistance profile of Mycobacterium tuberculosis complex isolated from pulmonary tuberculosis patients and their household contacts in central Ethiopia.

Background: There is a gap between tuberculosis (TB) infection and the onset of clinical TB disease, which makes identifying TB transmission dynamics a prominent challenge. Different reports were made on the concordance of drug-resistance profiles between the household contact and the purported index case. This study investigated the drug-resistance pattern concordance of the index-household contact pair in central Ethiopia.

Method: A laboratory-based cross-sectional study was conducted on Mycobacterium tuberculosis isolates identified from bacteriologically confirmed pulmonary TB patients and their household contacts (HHCs) in central Ethiopia from January to December 2023. Sputum specimens were collected from index cases and presumptive HHCs and examined using the Xpert Ultra assay, Xpert XDR assay, and Mycobacterium tuberculosis culture. Descriptive statistics were used to summarize the data.

Result: Among 902 TB symptoms screened HHCs of 303 index cases, 20.17% (182/902) had Presumptive TB, and 7.14% (13/182) developed active tuberculosis. In index cases, 23.52% (64 /272) showed resistance to at least one of the five first-line anti-TB drugs. The prevalence of mono-resistant to STR, INH, RIF, and PZA was: 2.20% (6 /272), 2.20% (6/272), 6.25% (17/272), and 1.47% (4/272), respectively. Any first-line anti-TB drug resistance was higher among relapse cases than new cases, at 41.67% (10/24) and 21.77% (54/248), respectively. Among the RR/MDR-TB cases tested with the Xpert MTB/XDR assay, 56.81% (25/44) cases showed resistance to INH. Among these 25 INH resistance samples, 5 had no melting point on the wild ahpc gene as well as on the ahpc gene mutant. In HHCs with positive cultures, 23.07% (3/13) displayed resistance to any first-line anti-TB medication. Only 69.23% (9/13) of HHCs had isolates that aligned with the pDST pattern of the index case for all five first-line anti-TB drugs.

Conclusion: Nearly one-third of the household contacts have discordant drug-resistance profiles from the index patients. This study offers compelling proof that it is not advisable to treat close contacts without DST results based on the DST results of the supposed source case. The low drug resistance rate to new oral second-line drugs in this study did not guarantee the absence of resistance to each drug.