Tracing the spread of drug-resistant TB

An international research team has, for the first time, used DNA sequencing to trace the fatal spread of multidrug-resistant tuberculosis (MDR-TB) between patients in the UK. Their study has been published in the journal Emerging Infectious Diseases.

TB is spread by inhaling tiny airborne droplets from an infected person, with its bacteria able to survive in the lungs for long periods without causing symptoms. While most infections can be treated with antibiotics, some forms are resistant to drugs. MDR-TB, which is resistant to at least two of the main treatments, has become more common in the UK, increasing from 28 cases per year in 2000 to 81 in 2012.

MDR-TB has thus become “a real problem”, said the study’s lead author, Dr Graham Cooke from Imperial College London. “It takes a lot of time, effort and resources to treat, and treatment is less successful.”

In 2010, the Health Protection Agency (now Public Health England) began performing genetic tests on samples of TB bacteria to help identify links between patients and better understand how infections are passed on. Dr Cooke and his fellow researchers used this genetic information to trace the source of infection in a 44-year-old British patient, who had never travelled abroad, who died of the disease in 2012.

The DNA profile of the TB bacteria sample was matched to that of a patient who had worked as a healthcare worker at Tugela Ferry Hospital in South Africa, the location of a serious outbreak of drug-resistant TB in 2005. The patient later moved to the UK to work.

Admission records established that both patients were admitted on the same medical ward in a UK hospital for eight days in 2008. The healthcare worker passed away that year, but the TB infection didn’t manifest itself in the second patient until four years later, when he was admitted to hospital and ultimately succumbed to the infection.

“Genetic sequencing enabled us to establish beyond reasonable doubt that a patient who died of multidrug-resistant TB caught the infection from another patient at a hospital in the UK,” said Dr Cooke. “Genome sequencing of pathogens is becoming part of routine practice for establishing transmission patterns for TB and other infectious diseases. This sort of analysis will help to improve our understanding of how diseases spread and identify more effective ways to stop them.

“In this case, the infection was traced to a healthcare worker. At a time when Ebola is in the news, this reminds us that healthcare workers are vulnerable to many infections and, if not diagnosed, have a high risk of passing them on.”

“The paper illustrates the importance of genetic profiling in identifying and pinpointing transmission and investigating outbreaks,” said Professor Alison Holmes from Imperial College London. “The development of more rapid diagnostics and molecular epidemiology will be invaluable in addressing the spread of infection and drug resistance.”

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