LONDON, June 8 -- Women in developing countries are less likely than men to test positive for tuberculosis because they don't know how to expectorate sputum properly.
In a pragmatic randomized trial in Rawalpindi, Pakistan, a few minutes of instruction in proper expectoration techniques increased the proportion of women who were smear-positive for TB by 63%, according to Mishal Sameer Khan, M.Sc., of the London School of Hygiene and Tropical Medicine here.
Sputum-submission guidance also increased the proportion of men who tested positive, but the difference from the control group wasn't significant, Khan and colleagues reported in the June 9 issue of The Lancet.
(American TB experts said that patients in the U.S. also may need instruction in how to raise secretions from the lower respiratory tract. Too often, said one authority, they provide saliva instead.)
The researchers enrolled 3,055 men and women suspected of having TB who came to Rawalpindi's Federal Tuberculosis Center for tests in 2005 from May through July.
Of those, 771 men and 749 women were randomly assigned to get a two-minute set of instructions on how to give a proper sputum sample and then were asked to provide a spot sample and an early-morning specimen taken upon awakening.
Patients in the control group were asked for the two samples only.
The instruction session explained the difference between sputum and saliva, emphasized the need for sputum, demonstrated the proper technique for spitting up sputum (three deep breaths, followed by a deep cough), and told patients to fill at least a quarter of the container.
The study found that:
Instructed women were more likely to test smear-positive than were women in the control group. The risk ratio was 1.63, with a 95% confidence interval from 1.19 to 2.22, which was significant at P=0.002.
13% of women in the instructed group, compared to 8% of those in the control group, were smear-positive.
Instructions were also associated with a significantly lower rate of saliva submission in the spot samples and significantly more women returning with an early-morning specimen (at P=0.003 and P=0.02, respectively).
There were no significant differences among the men, Khan and colleagues reported, although the rate of smear-positive samples tended to be higher among the instructed men than controls (11.7% versus 9.9%).
Overall, the intervention led to 49 additional cases being detected, the researchers said, with a cost of $2 per additional case.
The researchers noted that the intervention is cheap and easy to implement and therefore should be useful in resource-limited settings. They added that the large sample size and the real-world nature of the patient group imply that the results should generalize easily.
"Sputum-submission guidance is probably beneficial in settings where patients, particularly women, have little knowledge about tuberculosis and where saliva submission rates are high," they said.
The quality of the study is high, according to Bachti Alisjahbana, M.D., of Hasan Sadikin Hospital in Bandung, Indonesia and Reinout van Crevel, M.D., of Radboud University Nijmegen Medical Center in the Netherlands.
"Developing countries see too few studies, such as Khan's, that provide scientific evidence for decisions in health-service provision," they said in an accompanying editorial.
Combining sputum instruction with other interventions, such as the education of health professionals or more sensitive diagnostic methods, "might further improve the diagnosis of tuberculosis," they concluded.
The research was supported by the British Department for International Development. The authors reported they had no conflicts in interest. Also Drs. Alisjahbana and van Crevel said they had no conflicts. Primary source: The LancetSource reference: Khan MS et al. "Improvement of tuberculosis case detection and reduction of discrepancies between men and women by simple sputum-submission instructions: a pragmatic randomized controlled trial." Lancet 2007; 369: 1955-60.
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