According to a new UK-wide cohort study published online in the American Thoracic Society's American Journal of Respiratory and Critical Care Medicine, the incidence of TB (tuberculosis) diagnosis is substantially higher in new mothers after childbirth, indicating that this group of women represents a potentially new target group selected for screening.
In a collaborated study, researchers from the Health Protection Agency and the University of East Anglia, evaluated data obtained from the General Practice Research Database on all pregnant women between 1996 and 2008. The Database represents 5.5% of the UK population and contains records from 460 practices across the UK.
Dominik Zenner, degree consultant in public health of the Respiratory Diseases Department at the Health Protection Agency stated:
"Ours is the first primary care based cohort study to quantify the risk of TB during pregnancy and postpartum. Although we found a significantly increased risk of TB in the six months following pregnancy, but not during pregnancy, the risk during pregnancy is almost certainly also increased."
For their study, researchers estimated the incidence rates for TB during pregnancy, six months after birth and outside of pregnancy and adjusted incidence rate ratios (IRRs) in a retrospective cohort study using a model.
They also evaluated a nested self-controlled case series (SCCS) that was adjusted for all non-time-dependent confounders, like country of origin and ethnicity. In the SCSS evaluation, researchers identified pregnant women with TB from the cohort, and compared incidence rates (IRs) in pregnancy and after birth with rates outside pregnancy.
The cohort study included a total of 192,801 women with a total of 264,136 pregnancies. The researchers noted that from 177 TB cases during the study, 22 cases each occurred during pregnancy and within 180 days after giving birth. They established that the approximate TB rate for the combined pregnancy and post-birth period was 15.4 per 100,000 person years. This was substantially higher compared with the rate outside of pregnancy (9.1 per 100,000 person years, p=0.02). After the researchers adjusted for age, region and socio-economic status, they discovered the post-birth TB risk to be substantially higher than the TB risk outside pregnancy (IRR 1.95, CI 1.24-3.07), but noted no significant increase in women during pregnancy (IRR 1.29, CI 0.82-2.03).
The SCCS evaluation confirmed the researchers findings and after adjusting for all non-time bound confounders, the time-span of observation and patients' age they observed no significant increase to the risk outside of pregnancy, whereas the TB risk was substantially increased in women 6 months after giving birth (IRR 1.61, CI 1.01-2.58, p=0.04).
The study was subject to various limitations, such as observational design, and the fact that administrative delays between the diagnosis and recording of TB have occurred. Diagnostic delays may have occurred during pregnancy given that immunological changes during pregnancy gradually increase TB susceptibility and normalize gradually after delivery. All factors combined may account for the failure to demonstrate a substantially increased risk of TB during pregnancy.
Dr. Zenner concluded: "The incidence of TB diagnosis is significantly increased post-partum, probably reflecting an increase in TB incidence during pregnancy. Given our results, targeted screening of pregnant and post-partum women in high-risk groups may be warranted, given that delays in treatment initiation are associated with poorer outcomes for both mothers and their children."
Written by: Grace Rattue