Derek Thaczuk, Friday, January 05, 2007

A systematic review of studies in low- and middle-income countries has found reports of latent
TB infection among 33% to 79% of all health care workers in these settings. Most health care
facilities examined had no specific TB control measures in place. The review is published in
the January edition of the on-line journal PLoS Medicine.

Fully one-third of the world's population is latently infected with Mycobacterium tuberculosis.
About 10% of infected people develop active tuberculosis (TB), a potentially fatal infection.
Since TB is very easily spread by people with active pulmonary infection, health care workers
are at great risk for contracting it. In developed, higher-income countries, prevalence rates
of latent TB infection among health care workers range between 5% and 55%. Since the
introduction of widespread TB infection-control measures, the annual risk of infection in these
settings has dropped to between 0.1% and 1.2% (from 0.1% to 10% in studies published before
1995).

In lower-income countries, where 90% of the world's TB cases occur, there is very little money
for infection control. A research team from India, Canada and the US recently conducted a
systematic review of published studies to estimate the risk of TB among health care workers in
"low- and middle-income countries" (LMICs - defined as those with a gross national per-capita
income lower than $10,066 USD in 2004) in Africa, Asia, South and Central America. They found
that the prevalence of latent TB infection among health care workers in these countries was
reported as, on average, 54% (range 33% to 79%). Estimates of annual risk ranged from less than
1% to 14%. Certain work locations (e.g. emergency and TB inpatient facilities, and labs) and
occupations (e.g. nurses, radiology technicians and patient attendants) were at higher risk.

The team calculated that "after accounting for the incidence of TB in the relevant general
population, the excess incidence of TB. attributable to being a [health care worker] ranged
from 25 to 5361 cases per 100,000 people per year."

The researchers reached these conclusions by extracting data from 51 English-language studies,
published in 42 articles, and contacting TB experts worldwide. They acknowledge that "only
studies where there was a high incidence" may have been published, skewing the results higher,
and that the omission of non-English studies may have biased the results. (However, English
abstracts of several non-English studies showed comparable results.)

Another major limitation was the lack of data on latent TB in these countries at large, making
it difficult to compare health care workers to the general population. However, the review
showed that TB prevalence increased with time spent in the profession, likely reflecting
cumulative exposure, and incidence in health care workers was "generally higher than the
estimated TB rates in the general population."

The researchers concluded that risk reduction "should be a high priority because occupational
TB leads to the loss of essential, skilled [health care workers]", and that "well-designed
field studies are urgently needed to evaluation whether the TB-control measures that have
reduced TB transmission . in high-income countries will work and be affordable in LMICs."

HIV & AIDS Treatment in Practice special edition on TB infection control in health care
settings

Reference
Joshi R et al. Tuberculosis among health-care workers in low-and middle-income countries: a
systematic review. PLoS Medicine 3:e494:2376-2391, 2006.