Challenge of diagnosing TB

TB scientists say HIV infection and poor quality sputum specimens make it difficult to diagnose TB. This in turn contributes to the rapid spread of TB and drug resistance, especially in HIV-positive patients.

Night sweats; appetite loss and a bad cough are some of the symptoms indicative of TB. Normally, for TB to be diagnosed, a sputum or blood sample of a patient needs to be tested in a laboratory. The traditional method for laboratory diagnosis of TB normally takes seven to 14 days. But Violet Gabashane, Laboratory Manager at the National Health Laboratory Service (NHLS) in Braamfontein in Gauteng, says diagnosis can take longer if a patient is also HIV-positive.

"You will recall that HIV kills white blood cells. So now, you find that if the patient is HIV-positive and gets infected with TB, it does not stay in the lungs. It also spreads to other parts of the body.  So what does that mean? It means TB particles decrease from the lungs. And when they decrease, it becomes a problem for us to detect them. That is why it is not easy to diagnose TB from HIV patients," she said.

Gabashane says another contributing factor to the delay in diagnosing TB is the poor quality of sputum that is sometimes sent to laboratories.

"Some people are able to follow instructions carefully. But some don't. Instead of coughing up sputum into the sample bottles, they just put in saliva.  So, in that way it becomes a problem to diagnose TB," she said.

Dr Tony Moll is the Principal Medical Doctor at the Church of Scotland Hospital in Tugela Ferry in the Msinga area of KwaZulu-Natal, where 53 patients were diagnosed with Extensively Drug Resistant Tuberculosis in 2006. He says the delay in diagnosing TB, particularly drug resistant TB, can impede treatment and control efforts.

"The most difficult thing... is the long time it takes to actually diagnose MDR or XDR. And it's not a bedside diagnosis. You can't tell the difference between regular TB, MDR and XDR. It's only when the laboratory has actually cultured the sputum and grown the TB organism and challenged it against the different drugs. To get a diagnosis of XDR, it takes from six to eight weeks - and during that time, patients are mixed together," he said.

Dr Natalie Beylis, a consultant pathologist, says there is a need to reduce the number of days that are spent on diagnosing TB.

"The sooner you diagnose a patient with TB, the sooner you can start treatment. And treatment obviously makes them better and decreases mortality. But also from the public health point of view, treatment will make that patient less infectious. And then you will be able to stop the spread of TB in the communities," she said.

Gabashane says there is research underway looking at decreasing the number of days it takes to diagnose TB. However, "it is still in its early stages", she added.

According to the World Health Organization (WHO) statistics TB infects one million and kills an additional two million people worldwide every year.

 01.04.2008  Mabutho Ngcobo, Health-e news