06 August 2008

Sniffing out TB

An increadible machine that can literally "sniff" out TB is being developed, and Cape Town's own Desmond Tutu TB Centre at Tygerberg Hospital is part of this exciting project.

Imagine if you could breathe into a device that could tell you right then and there if you had tuberculosis (TB). Imagine the lives that can be saved and unnecessary infections spared with such a rapid diagnostic test. Imagine the money, time and manpower that can be applied to other areas of treatment and prevention of the disease.

Doctors and scientists from the Desmond Tutu TB Centre at Stellenbosch University Faculty of Health Sciences at Tygerberg and the Royal Tropical Institute in the Netherlands are developing just that – an electronic nose (or e-nose) that sniffs out TB from a breath sample. It's something that may change the destructive course of TB forever.

What is the e-nose?
The e-nose concept has only been applied to medical science in recent years, but other industries, for example the food industry, have been using electronic aroma-analysers for some time to test the quality of food and wine.

The e-nose machine works much the same as the human nose. It is fitted with various electronic sensors tuned into the particular smell of certain chemicals. A sample is fed into the machine to "smell" and if the sensors find traces of the chemical or volatile organic compound (VOC) (in this case VOC associated with a bacteria), the machine alerts the user.

Tygerberg project
The Royal Tropical Institute is currently developing the technology for an e-nose machine that will hopefully become a rapid, accurate, low-cost and non-invasive TB diagnostic tool.

However, as TB is a rare occurrence in the Netherlands, the Desmond Tutu TB Centre was brought on board to gather breath samples from TB patients in the Western Cape, where there is a very high TB prevalence.

These samples are used to test the machine and also to develop an “aromatic TB profile” from which the e-nose can detect the disease.

"We are using the technology from a developed country and implementing it into a developing country," says project co-ordinator at the Desmond Tutu TB Centre, Dr Mareli Claassens. "And we both benefit from the combined effort."

The project started in South Africa in April 2007 and will continue until the end of 2008. "We hope the machine will have been developed far enough by then," says Claassens. "If not, we'll have to extend the project."

How the sampling is done?
Breath samples are taken from TB patients already in the health care system at the Ravensmead, Uitsig and Elsiesriver clinics. "We have special thick plastic bags, each with a small pipe attached. The patient blows up the bag until it is filled with breath (including the volatile organic compounds specific to TB) – no sputum or spit," explains Claassens. "The bags are collected at the clinics and taken to the laboratory at Tygerberg Hospital where the air is pumped out and compressed into a special tube. From there, it's sent to the Royal Tropical Institute in the Netherlands."

Blood and sputum samples are also collected from patients and are used in collaboration with the “breath” samples to build up the e-nose's memory bank.

More about the machine
The e-nose machine is currently in the "proof of concept phase" that will determine if it can be developed into a feasible diagnostic tool. The aim is to create an affordable machine that can make a TB diagnosis within seconds, is between 90 and 95% accurate, compact and easy to use. The accuracy rate is above 80% at present.

Apart from the obvious benefits of saving time, money and manpower, the "breathalyser" type test is a non-invasive procedure which will improve on the traditional methods of taking blood and sputum samples.

It is particularly difficult to get sputum samples from children as they can't cough up sputum, which then has to be extracted from the stomach. This tedious and uncomfortable procedure involves extracting gastric washings with a nasogastric tube which goes through the nose, down the throat and into the stomach. Although this procedure doesn't hurt, it is rather uncomfortable.

"Should the e-nose be developed and implemented, it would be used on all patients – children and adults. But it (the e-nose) would particularly benefit children because it's non-invasive and the diagnosis of TB is so difficult in children with traditional methods," says Claassens.

At the moment it can take up to six weeks to get a TB diagnosis. The procedure can be invasive for the patient and requires lab time and is costly. In addition, the infected person can infect others during the time it takes for the diagnosis to be made.

"If it were implemented in South Africa, it would facilitate diagnosis, so people can get treated sooner. Fewer people would therefore be infected. And in turn, that could decrease TB prevalence in the country," says Claassens.

TB prevalence in South Africa
South Africa is ranked seventh on the World Health Organization's (WHO) list of High Burden Countries. Every year about 15 000 South Africans die from tuberculosis. WHO estimates that 66% of the South African population is infected with the tubercle bacillus and 370 000 new infections occur each year – 2% of which is of the multi drug-resistant (MDR-TB) strain.

(Wilma Stassen, Health24, February 2008)

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