There were nearly 500,000 cases of multi-drug resistant tuberculosis (MDR-TB) worldwide in 2006, according to a report released by the World Health Organization (WHO) on February 27th . This represented approximately 5% of all cases of TB.
The report also showed that there was a connection between MDR-TB and HIV. But the report’s authors think that poor infection control rather than “host” factors are the reason for this.
Extensively drug resistant TB (XDR-TB), which has resistance to second-line TB drugs and is associated with rapid disease progression and a high risk of death, was present in 45 countries.
Details of the report
Information on TB cases was collected from 81 countries and two regions of China, and the investigators were able to analyse data on an estimated 35% of all global reported smear-positive TB cases.
Amongst patients newly diagnosed with TB the prevalence of MDR-TB ranged from 0% in several western European countries to 56% in Baku, Azerbaijan. Fourteen of the settings with the highest rates of MDR-TB amongst patients newly diagnosed with TB were in the former Soviet Union.
Information was also included in the report on drug-resistant TB amongst patient who had had previously been treated for TB. Resistance to at least one TB drug ranged between 0% in some European countries and 86% in Tashkent, Uzbekistan. The setting with the highest proportion of MDR-TB cases was also Tashkent (60%).
WHO estimated that 20% of TB cases in 2006 had resistance to at least one drug, that 13% of cases were resistant to the key first-line drug isoniazid, and that 5% of TB patients had MDR-TB. This meant that there were almost half a million cases of MDR-TB in 2006. Half of these cases were located in India and China with 7% in the Russian Federation.
XDR-TB
The WHO report showed that 7% of reported MDR-TB involved cases of the often untreatable XDR-TB, with cases recorded in 45 countries.
In countries of the former Soviet Union, approximately 10% of MDR-TB cases involved XDR-TB. But there were significant variations in prevalence in these countries. In Armenia 4% of MDR-TB cases involved XDR-TB, but the figure was 24% in Estonia.
Wide regional variation in the prevalence of XDR-TB also appears to be present in South Africa. A report in 2007 showed that 6% of all MDR-TB cases involved XDR-TB, but the prevalence was much higher in KwaZulu-Natal at 14%.
MDR-TB and HIV
Seven countries provided information on MDR-TB and HIV. Data from Latvia and the Ukraine showed that any resistance to any TB drugs, as well as MDR-TB, was associated with HIV.
“This population-level association is a great concern for countries without accessible diagnostic networks in place, indicating that HIV-infected patients will not receive appropriate therapy quickly enough to avert mortality”, write the authors.
They also note “evidence suggests that the association between HIV and MDR-TB may be more closely related to environmental factors such as transmission in congregate settings rather than biological factors…it indicates that improving infection control in…health care facilities and prisons may be one of the most critical components in addressing dual infection.”
Gaps in knowledge
But the report may be providing an incomplete picture of the scale of the MDR-TB epidemic. The authors note that although Africa has more cases of TB than any other region in the world, only six countries contributed data to the survey. Many countries could not provide information as they lack expensive testing equipment and trained personnel.
“Without these data, it is difficult to estimate the true burden and trends in MDR-TB and XDR-TB in the region. It is likely there are outbreaks of drug resistance going unnoticed and undetected”, comment the authors.
More money needed
It is estimated by WHO that $4.8 billion is needed for TB control in low- and middle-income countries in 2008, with $1 billion for MDR-TB and XDR-TB. But there is a $2.5 billion short-fall for general TB programmes and a $500 billion shortfall for MDR-TB and XDR-TB efforts.
“The threat created by TB drug resistance demands that we fill these gaps”, said Dr Marcos Espinal of the Stop TB Partnership.
The WHO/IUATLD Global Project on Anti-tuberculosis drug resistance surveillance. Anti-tuberculosis drug resistance in the world: fourth global report. February, 2008.