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TB risk in prisons spills over to impact the wider population

12 Jan 2011

Paul Chinnock

Source: PLoS Medicine (see original article or PDF)

Citation: Baussano I, Williams BG, Nunn P, Beggiato M, Fedeli U, et al. (2010). Tuberculosis Incidence in Prisons: A Systematic Review. PLoS Med 7(12): e1000381.

Tuberculosis kills an estimated 1.8 million people every year, most of them in low- and middle-income countries. Prisoners – and people who work in prisons – are known to be especially vulnerable to the disease. The close contact in which prison inmates live facilitates transmission of Mycobacterium tuberculosis, the bacterium that causes TB. In addition prisoners’ higher rates of drug addiction, poor nutrition and other infections (most notably HIV), compared with the rest of the population, increase their level of vulnerability. Health care provision for prisoners is also poorer – sometimes very poor indeed.

However, it is not known how many people in prison become infected with M. tuberculosis or develop active TB each year compared with the general population. A newly published systematic review in PLoS Medicine has sought to address this question, and attempts also to calculate what percentage of latent TB infection (LTBI) and active TB in the general population is attributable to exposure in prison – the so-called population attributable fraction (PAF%).

Despite the widespread recognition of the problem posed by TB in prisons, the review reveals that there has been relatively little research on the topic. Only 23 studies met the researchers’ criteria for inclusion. Unhelpfully, the published review does not include a table summarizing the characteristics of these included studies. It is necessary, therefore, to seek out the individual papers to determine where each was conducted. Nearly half were studies in prisons in the USA. Three studies took place in Spain and three in Russia. There were two in Brazil, and one each in France, Israel and Côte d’Ivoire. The latter is the only low-income country represented in the data. Conspicuous by their absence are many countries with high TB burdens – for example, India, the Philippines, China and South Africa. WHO lists 22 countries as having the highest TB burdens; Brazil and Russia are the only two that appear in this review.

The researchers estimated the incidence of active TB in general populations using World Health Organization data; estimates of the incidence of LTBI in the general population came from the studies themselves. Next they calculated the ratio between incidence rates for LTBI and TB in prison and in the general population (incidence rate ratios or IRRs) for each study.

For both LTBI and TB, the IRRs varied considerably. The average IRR for LTBI was 26.4. That is, the average incidence of LTBI in prisons was 26.4 times higher than in the general population; the average IRR for active TB was 23.0. The PAF also showed much variation but on average the figure for TB in high-income countries was 8.5%; i.e. one in 11 cases of TB in the general population was attributable to within-prison spread of TB. In middle-to-low–income countries, the average PAF% was 6.3%.

It is clear from these findings that improvements in TB control in prisons would not only help to protect prisoners and staff from within-prison spread of TB but also reduce national TB burdens. But the review also demonstrates how poor our current understanding is of the problem. As an accompanying PLoS Medicine editorial [1] stresses, “even after a thorough search and rigorous analysis of the evidence, it is not possible to give accurate estimates of the increased incidence of TB in prisons over community rate”.

Living conditions and access to health care are notoriously poor in prisons in developing nations. There is therefore an urgent need to know more about the level of risk faced by prisoners and staff in those countries.

And most important we need to know how the situation can be improved, and which interventions are most effective in reducing rates of TB transmission within prisons.

Reference

1. The PLoS Medicine Editors (2010.) The Health Crisis of Tuberculosis in Prisons Extends beyond the Prison Walls. PLoS Med 7(12): e1000383. Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3006347/

2010 World Health Organization; licensee Public Library of Science (PLoS).

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