Conference on Retroviruses and Opportunistic Infections (CROI)

Conference on Retroviruses and Opportunistic Infections (CROI)

February 25, 2015
1 min read

Clustered transmission responsible for majority of XDR-TB cases

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SEATTLE — The majority of extensively drug-resistant tuberculosis cases in South Africa appear to result from transmission of clustered drug-resistant strains, according to data presented at CROI 2015.

“South Africa has among the highest burden of drug-resistant TB worldwide and has seen a fivefold increase in the number of [extensively drug-resistant tuberculosis (XDR-TB)] cases occurring each year,” N. Sarita Shah, MD, MPH, of the CDC, said during an oral presentation. “Prevention of XDR-TB is essential to reduce morbidity and mortality of this disease.”

Shah and colleagues examined the demographic, geographic and genotypic data of 377 XDR-TB patients (median age, 33 years; 57% female) diagnosed from 2011 to 2014 in the KwaZulu-Natal province in South Africa. Participants were interviewed about previous TB and HIV history, potential exposures and health care utilization, with medical records of prior treatments with first- and second-line TB medications examined as well to determine acquired resistance. Isolates of Mycobacterium tuberculosis underwent genotyping and targeted sequencing of nine resistance-conferring genes, and isolates from clusters identified in more than 20 patients underwent whole genome sequencing.

N. Sarita Shah

Six percent of the participants were health care workers, and 78% were infected with HIV, with a median CD4 count of 275 cells/mm3. At enrollment, 90% were on ART, and 79% had a viral load of less than 400 copies/mL. Twenty-one percent of participants had been previously treated for multidrug-resistant TB, and 7% had received fluoroquinolones or injected TB medications for other illnesses.

The researchers found that 87% of participants had an isolate belonging to one of 16 clusters, while 13% had isolates that were unique strains. One cluster accounted for 47% of all infections, confirmed to be highly clonal by full genome sequencing.

“The overwhelming role of transmission in the XDR epidemic in South Africa has highlighted the urgent need to refocus our attention on infection control and prevention,” Shah said. “This means implementing a combination of administrative, environmental and personal protection measures similar to what has been done to control TB in high-resource settings.” – by Dave Muoio.


Shah NS, et al. Abstract 92. Presented at: Conference on Retroviruses and Opportunistic Infections; Feb. 23-26, 2015; Seattle.

Disclosure: Shah reports no relevant financial disclosures.