TUBERCULOSIS THAT IS resistant to both first-line and second-line drugs is reaching “alarming levels” worldwide, according to a large international study.
The findings show a high prevalence of resistance (43.7 per cent) to at least one second-line drug among multidrug-resistant (MDR) TB patients from eight countries in Africa, Asia, Europe, and Latin America. Worse still, the study – published in medical journal The Lancet – found higher than expected overall levels of extensively drug-resistant (XDR) TB.
There are two types of drug-resistant TB:
- “MDR TB” – defined as resistant to at least two first-line drugs—isoniazid and rifampicin
- “XDR TB” – defined as resistant to isoniazid, rifampicin, a fluoroquinolone and a second-line injectable
“Most international recommendations for TB control have been developed for MDR TB prevalence of up to around 5 per cent. Yet now we face prevalence up to ten times higher in some places, where almost half of the patients with infectious disease are transmitting MDR strains”, warns Sven Hoffner from the Swedish Institute for Communicable Disease Control.
“Drug-resistant TB is more difficult and costly to treat, and more often fatal. 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,” said Tracy Dalton, the study’s lead author from the US Centers for Disease Control and Prevention (CDC).
“So far, XDR TB has been reported in 77 countries worldwide, but exact prevalence remains unclear,” she added.
The team used population-based data to quantify the extent of XDR TB and identify risk factors for being infected with a strain resistant to second-line drugs among people with MDR TB from Estonia, Latvia, Peru, the Philippines, Russia, South Africa, South Korea, and Thailand. Isolates from 1,278 adults with MDR TB were then shipped to the US Centers for Disease Controls and tested for suspecptibility to 11 first-line and second-line anti-TB drugs.
44 per cent resistance
The prevalence of drug-resistant TB varied widely from country to country according to the results, but the overall average detected was nearly 44 per cent of patients.
Resistance ranged from 33 per cent in Thailand to 62 per cent in Latvia, while – in a fifth of cases – resistance to at least one second-line injectable drug was identified, ranging from 2 per cent in the Philippines to 47 per cent in Latvia.
The proportion of cases with resistance to a fluoroquinolone was almost 13 per cent, with the lowest prevalence in the Philippines (7 per cent) and the highest in South Korea (32 per cent).
Meanwhile, XDR TB was detected in 6.7 per cent patients overall, with levels in South Korea (15.2 per cent) and Russia (11.3 per cent) more than twice the World Health Organisation global estimate for that period (5.4 per cent).
A key finding of the study was that the risk XDR disease more than four times higher in patients who had previously been treated – with previous treatment using second-line injectable drugs “consistently the strongest risk factor for resistance” .
Lifestyle factors were also linked to an increase risk, with unemployment, a history of imprisonment, alcohol abuse, and smoking all identified as factors associated with XDR disease.
“These results show that XDR TB is increasingly a cause for concern, especially in areas where prevalence of MDR TB is high. Nevertheless, information remains insufficient to give a clear view of the worldwide distribution and true magnitude of XDR TB,” aid Hoffner.
He highlighted the “urgent” need for updated information on MDR TB and an investigation of the trends, saying that “the true scale of the burden of MDR and XDR tuberculosis might be underestimated”.
The findings of the study are published in The Lancet