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Do people who have recovered from regular tuberculosis have greater immunity to multi-drug-resistant TB?

鈥� Surprisingly, given the historic nature and the incidence of tuberculosis in some parts of the world, the actual TB bacillus isn鈥檛 particularly infectious. It is thought that only 10 per cent of people who are infected develop active TB. The vast majority of people exposed to, or infected by, the bacillus will never go on to develop any clinical illness.

For the most part, you need to be exposed repeatedly in, for example, close family units or bad housing, with malnutrition and poor immunity possibly playing a part. In the pre-antibiotic era, a substantial proportion of people with active TB eventually recovered. Even today, a small subset of people with multi-drug-resistant TB will have apparent clinical recovery. So both innate resistance and acquired immunity against tuberculosis seem to exist.

Does a person who has been cured of TB have greater resistance to a new external source (which may or may not be multi-drug-resistant)? A study of more than 600 people with TB in Cape Town, South Africa, indicated that 18 per cent were reinfected. Of these, 14 per cent were reinfected with a different strain. Similar results have been found in trials in China.

It also appears that people who are reinfected are at a higher risk of developing active disease than someone who has never had the illness before. So exposure to TB doesn鈥檛 appear to boost resistance to the disease.

Gillian Coates, Trefor, Anglesey, UK

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This article appeared in print under the headline 鈥淩esistance not futile?鈥�