‘Beijing strain TB in Mumbai is drug-resistant’

The virulent Beijing strain that was found in most multi-drug resistant tuberculosis (MDR-TB) cases in Sikkim is a concern in Mumbai as well. Not only has the strain been identified in tuberculosis patients in Mumbai over the past decade, but in most cases it was also found to be drug-resistant.

“We have collected strains from tuberculosis patients in the last one year in Mumbai, and found that almost 95% are drug resistant,” said Dr. Nerges Mistry, director, Foundation for Medical Research, referring to a study that is still under way.

The Hindu on July 14 reported the growing concern of MDR-TB in Sikkim, which is recording almost the same proportion of drug-resistant cases as Mumbai, India’s TB capital.

The ICMR’s institute in Dibrugarh had over the last year studied 120 MDR-TB strains in patients from Sikkim and identified 70% of them as Beijing strains.

Drug mutation

Dr. Mistry said that the genome sequencing of the strains found in TB patients in Mumbai has shown a lot of drug mutation, making the cases more difficult to treat. However, there is no data yet on the strain’s prevalence and Dr. Mistry said there was a need for surveillance to map the numbers.

The reason why tuberculosis experts are worried is because the drug-resistant Beijing strain has an enhanced fitness “in terms of their ability to grow as compared to the drug-sensitive strains,” noted a study co-authored by Dr. Mistry and published by the reputed Elsevier . It further noted that the Beijing genotype was known to be associated with several outbreaks across the world “implying mechanisms which permit its predominance even in the presence of other competing strains”.

“This highlights the virulent nature of the strain and its high transmission efficiency across different continents and thus its inherent ability to multiply faster in the presence of several strain types,” the study says.

Studies published over the years have recorded the presence of the Beijing strain in Mumbai. About a decade ago, doctors at P.D. Hinduja Hospital had reported a high frequency (35%) of the Beijing genotype among the MDR-TB cases in a study published in Clinical Infectious Diseases journal.

The high figure was, however, attributed to the hospital being a tertiary care facility that largely gets cases not responding to the treatment.