Tuesday, December 16, 2008

Tuberculosis - hysteria in development

There was a letter in the Straits Times talking about the problem of TB is schools and the re-emergence of multidrug resistant TB etc... This is a bit of hysteria in the making, fueled somewhat by the Ministry of Health recently announcing it had place TB on the IDA (Infectious Diseases Act) Schedule 6 bugs list.

Hysteria? Yeah....because TB isn't that much of a problem really. We already have a TB immunization programme at birth (BCG; Baccille Calm
ette-Guerin). This confers a certain degree of immunity throughout childhood. Its efficacy wanes as the child gets older as is variably present in adulthood. We used to re-vaccinate at about 12 years old, but apparently this practice was discontinued in 2001 because of doubtful value of the program in protecting against future TB.

Most of the TB cases are in the elderly and do not represent new infections. Rather, they are a re-activation of what is called latent TB. Most of us, regardless of our 'immune status' are exposed to TB and go around carrying TB bug
s in our bodies. Mostly these are sleeping dragons that don't bother us. However, when our immunity falls, these sleeping dragons are reactivated. Common causes for a fall in immunity are HIV, cancer and the use of immuno-suppressive drugs. It is therefore highly unlikely most of us will develop active TB sitting next to a patient with active disease.

What about the
multidrug resi
stant TB problem? It seems to be a developing problem. Like all bugs, when they are exposed to inconsistent and incomplete treatment, the TB bacteria develops resistance to the drugs used. Fortunately this seems to result in rather wimpy bugs that are not very virulent and infectious. They seem to be a problem mostly for populations with reduced immunity such as those patients with HIV.

All in all, the problem of TB is not anything to lose sleep over. The incidence in Singapore is only about 35 per 100,000, i.e. about one infection out of every 3,000. If you consider these are mostly re-activated cases....it is really not that big a problem. The age group affected is mostly elderly (peak 40-60 yrs old), but like all distributions, there is a tail, and some young people with reduced immunity may succumb to the infection.
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Regardless of the MOH recent announcement of an increase in TB..
..(those are only projected numbers based on only 6 months of data, and the year is not over yet)....the trend over the last 40 years is a major and consistent reduction in TB incidence with no evidence of a reversal.

Hysteria? Definitely!

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What is a curious phenomenon though is the differential ethnic risk for TB...Malay > Chinese > Indian. I can't really explain this.

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