Mercedes Becerra

Early in her public health career, when epidemiologist Mercedes Becerra was a graduate student and just beginning her work with Socios En Salud, PIH’s sister organization in Peru, one of her primary responsibilities was to serve as a translator.

“I would sit between Paul [Farmer] and each patient, listening to stories,” she said. “Because I was invisible, I heard these amazing and detailed exchanges about people’s home lives, how TB had affected them directly, how it had affected their families, how so many had lost loved ones to TB,” she said. “That experience was the seed that grew into this study.” Dr. Becerra, a senior TB specialist at PIH and Assistant Professor of Social Medicine at Harvard Medical School, is lead author of a report (“Tuberculosis burden in households of patients with multidrug-resistant and extensively drug-resistant tuberculosis: a retrospective cohort study”) published in the January 2011 issue of The Lancet. 

Between September 1996 and September 2003, a PIH team of local Peruvian staff visited nearly 700 households in Lima to complete interviews. Each of these households was home to at least one patient who had been treated by the PIH program because the patient was sick with a strain of multidrug-resistant tuberculosis (MDR-TB) or extensively drug-resistant tuberculosis (XDR-TB). The study had two principal findings. First, persons living with these patients--their “household contacts”--had significant rates of tuberculosis disease themselves. Similar rates have been recorded in prisons and holding centers in Siberia. Second, when these household contacts had their TB strains tested for susceptibility to TB drugs, 90% also had MDR-TB strains themselves.

While the comparison to Siberian prisons may startle, the conclusion may not be as surprising: TB is transmitted through the air, and many of the families interviewed were living in small spaces, sometimes with poor ventilation. However, treating patients in their homes is still preferable to secluding them away from their families in medical facilities, said Dr. Carole Mitnick, a co-author of The Lancet study. "In most places in the world, hospitals are not equipped to protect other patients and health care workers from active TB or other airborne diseases," said Dr. Mitnick. "So even if people were hospitalized, this would put the most vulnerable people at risk--those who already have compromised immune systems--as well as health care workers." In addition, most transmissions actually occur even before an initial TB diagnosis is made, she added. 

In the study, Dr. Becerra, Dr. Mitnick, and the other authors (all affiliated with PIH, the Department of Global Health and Social Medicine at Harvard Medical School, and the Division of Global Health Equity at Brigham and Women’s Hospital) make some new observations about the arc of this disease, and offer recommendations to counter the burden it places on family and community members.

For example, international guidelines recommend that TB programs screen patients’ households for others with TB, but Becerra says this is not always a priority. “It can be difficult for local health staff to systematically implement TB contact investigations, because of immediate limits on resources and time,” she said. “It is difficult to prioritize going into the community to look for sick people when there are sick people who require TB treatment already at the clinic.”

Nevertheless, Becerra says this is an essential step. “Contact investigations should be done for all TB patients. Patients with active TB require prompt treatment, but those with latent [sub-clinical] TB infection who are at high risk for developing active TB must also be identified so that they can receive preventive treatment. This is the standard of care in the U.S. and in other countries where TB elimination is the goal.”

Furthermore, said Becerra, “in some parts of the world, TB patients who live with patients who have drug-resistant TB are treated with first-line TB drugs, as if they did not have this known risk. This puts them at risk, in turn, for bad outcomes: either death or ‘treatment failure,’ which means they survived the incorrect treatment but may have an even more resistant strain of TB.” Becerra says the take-home message is that if a patient has active TB, and is a close contact of someone known to have drug-resistant TB, that patient “should be treated as if they have drug-resistant TB disease until there is microbiological evidence that they do not.”

 
 

Community health worker visiting a patient at her home.

These PIH researchers also found that conventional wisdom about the length of time to monitor and follow these household contacts--two years--may not be enough. “We found that even after resistant TB patients were treated, the risk to others in their households remained high, even four years later,” said Becerra.

According to the authors, “more work is needed to establish for how long a contact should be monitored and the optimum frequency and methods with which to monitor [and]…more research is needed to identify the best strategies to monitor households after an initial visit.” The World Health Organization estimates that 440,000 people had MDR-TB worldwide in 2008, and that a third of them died. WHO also calculates that almost 50% of MDR-TB cases worldwide occur in China and India.

See the study in The Lancet.

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