Cases of tuberculosis that are resistant to virtually all drugs currently available to treat the disease are increasing at an alarming rate around the world, according to a study.
The paper, in the Lancet medical journal, shows that nearly half (47%) of TB cases that were already resistant to the two basic antibiotics used as standard treatment were also resistant to one of the second-line drugs that doctors try when the standard combination fails. The problem was worst in Latvia, where 62% of multi-drug-resistant TB (MDR TB) was not susceptible to at least one second-line drug.
The researchers also found a worrying increase in cases that were resistant to the entire class of oral second-line antibiotics known as fluoroquinolones, as well as one of the injectables – which is the criteria for being categorised as extensively drug-resistant (XDR TB). Overall, they found that 6.7% of patients with drug-resistant strains had XDR TB, which is very hard and expensive to treat and takes years rather than months in affluent nations.
In poorer countries, the necessary treatment is not available. The highest rates of XDR TB were in South Korea, at 15.2%, and Russia, at 11.3%.
Drug-resistant tuberculosis has spread around the world and has now been identified in 77 countries, but many of the worst-hit have inadequate laboratory diagnostic capacity and poor data collection so the exact prevalence is difficult to know.
The survey, by the US Centres for Disease Control and Prevention, found that XDR TB was most likely to develop when treatment for MDR TB had not been properly completed. It found that the risk of XDR disease was more than quadrupled in previously treated patients. Previous treatment with second-line drugs was consistently the strongest risk factor for resistance to these drugs.
"Drug-resistant TB is more difficult and costly to treat, and more often fatal," said Tracy Dalton, the study's lead author. "Internationally, it is particularly worrisome in areas with fewer resources and less access to effective therapies. As more individuals are diagnosed with, and treated for, drug-resistant TB, more resistance to second-line drugs is expected to emerge."
She added that social factors needed to be taken into account in the care of TB patients, who were more likely to develop resistance to second-line treatment if they were unemployed or had a history of imprisonment, alcohol abuse and smoking.
Sven Hoffner from the Swedish Institute for Communicable Disease Control said new information on the spread of drug-resistant TB was urgently needed. "Most international recommendations for TB control have been developed for MDR TB prevalence of up to around 5%. Yet now we face prevalence up to 10 times higher in some places, where almost half of the patients with infectious disease are transmitting MDR strains," he said in a commentary published with the paper in the Lancet.
The most recent estimates on drug resistance from the World Health Organisation suggest that around 9% is XDR TB. Dr Karin Weyer of the WHO's Stop TB Partnership said she welcomed any new data emerging but warned that in all but Estonia and Latvia, the studies were centred on specialist MDR TB referral centres and were not necessarily representative of the epidemic in each of the eight countries.
"The findings apply to the catchment areas around those centres, but you can't infer that the results are population-based and representative of the whole country," she said.
She saw the study as a wake-up call, however. "If you don't manage MDR properly, you end up with XDR," she said.
Dr Mel Spigelman, the chief executive of TB Alliance, which is working to develop new drugs to fight the disease, said the findings further confirmed the urgency of addressing the TB epidemic. "Specifically, these data reflect both the inadequacies of current TB treatments and the ability of drug-resistant TB to spread from person to person," she said.
"Faster-acting, simpler, more affordable, novel therapies are crucial and have the potential to treat both drug-resistant and drug-sensitive TB, improving adherence to treatment and expediting scale-up of suitable, cost-effective treatment, especially of drug-resistant TB."
New treatments were in the pipeline, but money and political will would be needed to make them reality, he said.
This article originally appeared on guardian.co.uk
