The Mangyan and MDA: Uncovering Social Barriers in Mindoro Oriental

In order to get the right answers, you have to ask the right questions. This sounds like common sense, but sometimes it can be easier said than done, particularly when the right questions do not appear to be related to the greater research question. This was the case in a study to strengthen the transmission assessment survey, or TAS, for lymphatic filariasis in the Philippines in 2017. By adding a single question to her survey, Dr. Leda Hernandez and her team at the Philippines Department of Health uncovered social barriers to mass drug administration that undermined the efficiency and effectiveness of the national lymphatic filariasis elimination program.

A collaborative effort of the Philippines Department of Health, the Centers for Disease Control and Prevention, and the Neglected Tropical Diseases Support Center (NTD-SC), the study did not have social science as its primary objective. Instead, it was part of a larger, multi-country effort to strengthen the strategy for assessing ongoing transmission of lymphatic filariasis (LF) after several rounds of mass drug administration (MDA). The current “gold standard” for this is the World Health Organization-recommended TAS, a standardized and statistically rigorous method, which serves as the tool for determining when it is safe to stop MDA.

The TAS is also used as a surveillance tool; repeated at 2-3 year intervals to ensure that transmission has not resumed. “It is unusual, but possible for an area to pass TAS the first time, but fail a subsequent TAS,” explains Katherine Gass of the NTD-SC. “This could be due to an increase in transmission or it could be that the original TAS failed to detect a signal by chance.” The latter scenario is of concern to national LF programs, because a false “passing” grade can lead to programs stopping MDA prematurely, thereby undermining elimination efforts. 

In a context like the Philippines, an archipelago of over 7,000 islands, assessing transmission levels can be a particular challenge. The physical constraints of the Philippines create many unique endemic zones. LF is endemic in 46 of 81 provinces in the Philippines, and while the Philippines National Filariasis Program (PNFP) began implementing MDA of diethylcarbamazine (DEC) (6mg/kg) and albendazole (ALB) (400 mg) in 2000, progress in some of these regions has proven challenging.

One province where LF transmission is still active is Mindoro Oriental, a relatively small province with a population of 844,000 people. Mindoro Oriental passed its first round of TAS in 2012, but only barely. Of the 3,080 children sampled, 15 tested positive for LF. This result technically “passes” because the number of positive cases was below the threshold of 18, but the margin was so small that the Evaluation Unit (EU) was flagged as a potential risk. TAS was repeated in 2015, and this time Mindoro Oriental failed.

Dr. Leda Hernandez Enter Dr. Leda Hernandez, Division Chief for the Department’s Infectious Disease Office in the National Center for Disease Prevention and Control. Dr. Hernandez saw the TAS results in Mindoro Oriental as an opportunity for operational research to improve the strength of TAS. In 2017, she partnered with the NTD-SC research team to investigate potential programmatic reasons for the TAS 2 failure on the island and to identify hotspots of ongoing transmission.

Dr. Hernandez also had a hunch. With 25 years of experience working with the national LF program, she had a unique understanding of regional challenges – epidemiological and social. She asked the research team to incorporate additional questions not generally incorporated in a TAS questionnaire to capture data on social factors in Mindoro Oriental. She was curious about whether a person’s ethnicity correlated with LF infection. In particular, she was interested in the large indigenous population on the island, and whether or not members of this group were more likely to test positive.

The results were striking. Of all parameters collected in the survey, ethnicity had the strongest correlation with probability of positive test results. It was also one of two parameters that proved statistically significant in the regression analysis. A subject identified as indigenous (Mangyan) was 66.9-76.5% more likely to be infected than a non-indigenous subject (majority Tagalog). 

These statistics imply some kind of barrier to access, but further research is needed to distinguish between incomplete coverage and incomplete compliance. Were the indigenous peoples in Mindoro Oriental not offered the drugs, or did they choose not to take them? The explanation could be as simple as the seasonal calendar of the Mangyan, which led more people to be away from their barangays at the time of MDA. Alternatively, these preliminary results could provide insight into a greater, systematic inequity.

“Questions can lead to more questions,” explains Dr. Hernandez. “The key is the zestful pursuit to find the answers which will guide the program to develop strategies and approaches that appropriately addresses the challenges of the future for the greater good of all.”

Photos:  1. Leda Hernandez (far left) assists in an interview  (Katherine Gass/Neglected Tropical Diseases Support Center)

                2. Leda Hernandez (center) oversees health workers in the field  (Katherine Gass/Neglected Tropical Diseases Support Center)