Monitor and Evaluate Progress toward Elimination/Control of NTDs
CDC works to help monitor and evaluate progress and impact of programs designed to control and eliminate disease. Control efforts focus on diseases that have not been targeted for elimination, to reduce transmission and treat affected individuals. Elimination efforts focus on human diseases that have been targeted for interruption of transmission. Each program has specific guidelines for mapping (assessing the burden of disease in a specific area), making decisions about implementing mass drug administration (MDA), and changing the frequency of (or stopping) MDA.
CDC in Action: Helping Eliminate Lymphatic Filariasis (LF) from American Samoa
In 1997 the World Health Assembly passed a resolution calling for the global elimination of lymphatic filariasis (LF) as a public health problem by the year 2020. Shortly afterwards, the Pacific Program for the Elimination of Lymphatic Filariasis (PacELF) was formed and called for elimination of LF in the Pacific Region through a strategy of annual rounds of mass drug administration (MDA). Results from surveys conducted in 1999 established American Samoa as one of the countries with the highest filarial infection levels in the Pacific Region and the only U.S. territory endemic for LF.
Since treatment began in 2000, CDC has assisted the American Samoa Department of Health (DOH) with surveys to monitor the progress of the LF program. Evaluations conducted in 2001 and 2003 showed that infection levels had not changed significantly since the beginning of the program. In response to these findings, CDC experts helped to re-examine and modify the communication and drug distribution strategies for the LF program. By 2006, a dramatic decline in infection levels was seen.
In 2007, with assistance from CDC, the DOH conducted a nationwide survey and found significant progress had been made toward the elimination of LF in American Samoa. As a precaution, the DOH made the decision to conduct another round of MDA the following year. Current WHO guidelines provide instruction for conducting a Transmission Assessment Survey (TAS) to determine whether MDA can be stopped in an area that has had at least five rounds of annual drug distribution. In collaboration with the American Samoa Departments of Health and Education, American Samoa Community College and The Task Force for Global Health, CDC conducted a TAS in February 2011. Results from this survey indicated that infection prevalence was below the threshold required for mass treatment. As a result, an official recommendation to stop MDA was made. In an effort to identify any residual infections in adults in American Samoa, arrangements were made to implement LF screening in routine well checks and new employment health screenings. Individuals will be given the opportunity to be tested and if found to be positive will be offered treatment.
CDC in Action: Guiding Countries on What to do After MDA is Stopped
Most countries where LF is widespread have instituted WHO-recommended mass drug administration (MDA) programs to help stop the spread of infection and interrupt transmission. WHO has produced clear guidelines for how to implement MDA programs, including how to assess if transmission has been lowered so MDA can be stopped. Less defined, however, are the steps a country must take once MDAs are stopped.
Togo was among the first African countries to institute a national control program for LF-elimination and has recently met WHO benchmarks for stopping MDA. CDC is working with the National Program for Elimination of LF (NPELF) in Togo to pilot a post-MDA program for LF. This program is intended to confirm elimination of LF transmission in Togo and to ensure if there are any additional cases, they would be quickly detected and measures taken to prevent resurgent transmission. This approach includes (1) a sustainable, laboratory-based, nation-wide LF monitoring system, (2) nation-wide re-mapping, and (3) active follow-up of reported cases of LF.
The Surveillance System
The LF surveillance system in Togo, which includes more than 40 national labs, takes advantage of the fact that one test for LF is similar to a test performed to detect malaria. CDC worked with the Togo national program to train lab technicians who routinely view blood slides to identify malaria psarasites, to simultaneously evaluate slides for the presence of LF parasites. After the first two years of the surveillance program, the program had tested slides from 8050 persons from 1200 villages across the country. Mapping the residences of the patients tested showed that there were some regions of the country that were not being tested well—presumably because villagers in those remote areas of the country were unlikely to travel to one of the surveillance hospitals CDC is now working with the program in Togo to institute testing at remote health outposts in these regions. The collaborators continue to explore other alternatives, such as whether testing of donated blood would be a feasible option for conducting LF post-MDA surveillance.
The first step in implementing an LF-elimination program is to conduct nation-wide mapping for the disease to identify which areas have enough cases to warrant treatment with MDA. For Togo, this mapping was conducted in 2000 and found that MDA was needed in seven of the 35 districts in the country. By 2006, all seven of the LF-endemic areas identified in 2000 had been treated for at least 5 years with MDA. Each of these areas was closely monitored. Until a nationwide surveillance system was established in 2006, however, no testing for LF was conducted in the other 28 districts. To ensure transmission of LF was stopped, CDC assisted the NPELF to repeat a national mapping in 2010. In total, 23 potential cases were identified among 7,800 persons tested in 78 villages throughout the country.
Follow-up of Identified Cases
Because the purpose of national surveillance for LF is to identify areas of the country where LF is still prevalent, each case identified in the laboratory-based surveillance system or the nationwide re-mapping prompts a follow-up community investigation. CDC worked with NPELF to develop an appropriate method to follow-up each identified case. This includes re-testing each person testing positive for LF, and, if infection is confirmed and the person tested resides in Togo, testing at least 500 members of their community. Follow-up of the two cases identified so far by the national surveillance system found no other positive members of the cases' communities and follow-up of the cases identified by the re-mapping is still in progress.