Results from a WHO surveillance survey found no evidence that Chlamydia trachomatis reemerged after a program of mass antibiotic distribution ended.1
Researchers added that a low prevalence of antibodies to Chlamydia trachomatis pgp3 (2.4%) is further evidence of interruption of transmission.
A total of 2021 children and 4000 adults from 2 Nepalese districts, Dang and Dailekh, participated in the surveillance survey. Prevalence of follicular trachoma (TF) was 0.1% in Dang (95% CI; 0.03% to 0.55%) and 0.2% in Dailekh (95% CI; 02% to 0.72%). Researchers found one case of infection in Dailekh district.
Researchers tested 794 children for antibodies to chlamydia antigen pgp3. Among 1 to 4 year-olds, antibody positivity was 2% in both districts. Prevalence of antibody positivity was slightly higher among 9-year-olds, but the difference was not statistically significant.
“Unlike just looking to see if there’s infection or clinical disease right now, the antibodies should tell us whether this child has ever experienced exposure to trachoma,” said Sheila West, PhD, the El-Maghraby Professor of Preventive Ophthalmology and Vice Chair for Research at the Wilmer Eye Institute, with a joint appointment in the Department of Epidemiology at the Johns Hopkins Bloomberg School of Public Health. “If a child has little to no exposure and was born after the program stopped, then we can hopefully say that there’s been an interruption of transmission.” Dr West was part of the research team that conducted the survey.
Researchers found 1 new case of trichiasis (TT) among the adult participants. Prevalence of TT was 0 in Dailekh and 0.5/1,000 in Dang.
Officials with WHO note that trachoma, a chronic conjunctivitis caused by repeated episodes of Chlamydia trachomatis, is the world’s leading infectious cause of blindness worldwide. The WHO is part of the Alliance for Global Elimination of Trachoma by the year 2020, and recommends the SAFE strategy (Surgery for trichiasis, Antibiotics to reduce infection, Facial hygiene, and Environmental change for sustainable interruption of transmission) to stop the spread of trachoma.
Participating countries are asked to map suspected trachoma endemic districts to determine the prevalence of TF and TT, and institute SAFE where prevalence of trachoma is 5% or more in children aged 1 to 9 years and TT is 1/1000 or more of the total population.
Impact assessments are conducted after 3 to 5 years of SAFE interventions begin. If those impact assessments show that the interventions have successfully reduced TF below 5% and TT <1/1000 in those populations, SAFE activities, especially mass drug administration, can end.
WHO recommends that surveillance surveys are conducted to make sure trachoma has not emerged following the end of the antibiotic distribution. In this case, researchers randomly selected 20 clusters within the 2 districts. Residual TF was 1.1% at the last impact survey.
Within each district, 20 clusters of 150 to 300 people were randomly selected for the surveillance survey. Fifteen districts were randomly assigned to have a test for infection and test for antibodies. The remaining 5 had the clinical survey alone.
Scott Nash, PhD, program epidemiologist for the Trachoma Control Program at The Carter Center, said the results show both a clear win for the SAFE program and illustrate the importance of surveillance.
“To have gone from a prevalence of 11% or 12% to below the threshold of 5% and to have kept it there, I would definitely say this is a success story for this area of Nepal,” Dr Nash said.
“These results definitely stress the importance of surveillance,” he added. “We have seen in other areas that recurrence is possible. It’s a great strategy to move toward formalizing these surveillance guidelines. These areas did not receive medication for up to 4 years and yet very few cases of trachoma were found and now this area can move toward certification.”
Dr West said that Nepal is conducting final surveillance surveys nationwide and, as soon as next year, may be able to demonstrate to the WHO that it has achieved elimination goals in all of the country’s 20 districts where trachoma was endemic.
“Trachoma is relatively difficult to transmit–it’s not like measles or smallpox. For chlamydia, the potential for transmission is low enough that once you get it to a certain point, it seems to disappear on its own,” she said. “If we see clinical disease at 0.1%, that’s well within a margin of diagnostic error and we don’t worry about it coming back.”
- Zambrano AI, Sharma S, Crowley K, Dize L, Muñoz BE, Mishra SK, et al. The World Health Organization recommendations for trachoma surveillance, experience in Nepal and added benefit of testing for antibodies to chlamydia trachomatis pgp3 Protein: NESTS Study. PLoS Negl Trop Dis. 2016; 10(9):e0005003.