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Nosocomial transmission responsible for XDR-TB outbreak in South Africa

An epidemic of extensively drug-resistant tuberculosis in Tugela Ferry, South Africa, was the result of interconnectedness that allowed multiple generations of nosocomial transmission, according to data reported in The Journal of Infectious Diseases.

“Rather than an isolated outbreak that can be traced back to a single index case, conditions in South African Hospitals are allowing for multiple generations of transmission, which in turn allows for the propagation and expansion of the epidemic,” Neel Gandhi, MD, associate professor of epidemiology and infectious diseases at the Rollins School of Public Health at Emory University, told Infectious Disease News. “Without comprehensively addressing infection control in health care facilities, it will be difficult to bring the current epidemic under control.”

Neel Gandhi

From 2005 to 2009, there were 516 cases of XDR-TB diagnosed in Tugela Ferry, and most of the patients were also infected with HIV. Because of the similarities between this outbreak and outbreaks of multidrug-resistant TB in the 1990s, the researchers investigated the role of nosocomial transmission in the current epidemic.

They conducted a retrospective, observational study of patients diagnosed with XDR-TB from 2005 to 2006. The study involved reviewing patients’ medical records, identifying epidemiologic links between the patients, genotyping the TB isolates and determining the social network of transmission.

The study included 148 patients with XDR-TB and 98% were coinfected with HIV. Almost all of the patients (93%) were hospitalized while infectious. Before XDR-TB diagnosis, 113 patients were hospitalized at least once, of whom 80 were exposed to at least one infectious patient with XDR-TB. The genetic analysis showed that there was one predominant strain family cluster (ST60) for 92% of the isolates. The KZN strain cluster accounted for 96% of the ST60 isolates.

Among 51 patients in the ST60/KZN cluster, the researchers established an epidemiologic link for 42 of them. The patients showed a high degree of interconnectedness. There were as many as three generations of transmission among men and five generations of transmission among women.

“In addition to examining the role of transmission in hospitals, we have expanded our investigation to include community settings,” Gandhi said. “Additional studies are currently underway to identify other potential sites of transmission (e.g., schools, bars, churches, etc.), as well as to better understand whether any genetic alterations are occurring to allow the XDR-TB strains to become more transmissible or pathogenic.”

Disclosure: The researchers report no relevant financial disclosures.

Neel Gandhi, MD, can be reached at 1518 Clifton Road, CNR 3031, Department of Epidemiology, Rollins School of Public Health, Atlanta, GA, 30322; email: neelgandhi@alumni.williams.edu.