Implications for annual retesting after a test-and-not-treat strategy for onchocerciasis elimination in areas co-endemic with Loa loa infection: an observational cohort study

Abstract

Summary Background A test-and-not-treat (TaNT) strategy has been developed to prevent people with high concentrations of circulating Loa loa microfilariae (>20 000 microfilariae per mL) developing serious adverse events after ivermectin treatment during mass drug administration to eliminate onchocerciasis. An important question related to cost and programmatic issues is whether annual retesting is required for everyone. We therefore aimed to investigate changes in L loa microfilarial densities during TaNT campaigns run 18 months apart. Methods In this observational cohort study, we assessed the participants of two TaNT campaigns for onchocerciasis. These campaigns, which were run by a research team, together with personnel from the Ministry of Health and community health workers, were done in six health areas (in 89 communities) in Okola health district (Cameroon); the first campaign was run between Aug 10, and Oct 29, 2015, and the second was run between March 7, and May 26, 2017. All individuals aged 5 years and older were invited to be screened for Loa loa microfilaraemia before being offered ivermectin (unless contraindicated). L loa microfilarial density was measured at the point of care using the LoaScope. All those with a L loa microfilarial density of 20 000 microfilariae per mL or less were offered treatment; in the first 2 weeks of the 2015 campaign, a higher exclusion threshold of 26 000 microfilariae per mL or less was used. At both rounds of the intervention, participants were registered with a paper form, in which personal information were collected. In 2017, we also recorded whether each individual reported participation in the 2015 campaign. The primary outcome, assessed in all participants, was whether L loa microfilarial density was above or below the exclusion threshold (ie, the criteria that guided the decision to treat). Findings In the 2015 TaNT campaign, 26 415 people were censused versus 29 587 people in the 2017 TaNT campaign. All individuals aged 5 years and older without other contraindications to treatment (22 842 people in 2015 and 25 421 people in 2017) were invited to be screened for L loa microfilaraemia before being offered ivermectin. In 2015, 16 182 individuals were examined with the LoaScope, versus 18 697 individuals in the same communities in 2017. 344 (2·1%) individuals were excluded from ivermectin treatment because of a high L loa microfilarial density in 2015, versus 283 (1·5%) individuals in 2017 (p<0·0001). Records from 2017 could be matched to those from 2015 for 6983 individuals (43·2% of the 2015 participants). In this cohort, in 2017, 6981 (>99·9%) of 6983 individuals treated with ivermectin in 2015 had L loa microfilariae density below the ...

Feasibility of Onchocerciasis Elimination Using a “Test-and-not-treat” Strategy in Loa loa Co-endemic Areas

“…In the second round, participation was higher and varied between 60.5% and 78% of the total population. [8] Another TaNT campaign conducted in 2017-2018 in the neighboring Soa health district and involving local health personnel and community volunteers showed an overall participation of approximately 66% in rural settings. [21] Urban and semi-urban areas show consistently lower rates of participation.…”

“…However, observations from the second TaNT round in Okola showed that the exclusion dropped from 2.1% to 1.5% within 18-months. [8] In a sensitivity analysis, we explored the impact of a decreasing exclusion rate. To match the observed change, we assumed an exponential drop (rate: 0.22 per year) in the first 10 TaNT rounds and no exclusion due to high loiasis MFD in the following rounds.…”

“…Of the individuals treated with ivermectin in the first round, 99.97% remained below the risk threshold, indicating that those individuals could have been safely retreated without retesting. [8] While the TaNT strategy has been successfully piloted in Cameroon, it remains unclear whether elimination of onchocerciasis is possible using this strategy and how long the program would have to be continued. We address these questions by mathematical modelling.…”

Test-and-not-treat: importance for mass drug administration

“…In The Lancet Infectious Diseases, Sébastian Pion and colleagues 8 compared microfilarial counts between two MDA campaigns that were run 18 months apart, to evaluate the necessity of obtaining microfilarial counts from the same patient before each MDA. Their results showed that, of the 6983 individuals for whom complete data were available, more than 99•9% of those with a safe L loa microfilarial count who were treated with ivermectin in 2015 had a L loa microfilarial density below the threshold associated with serious adverse events on repeat testing 18 months later.…”

“…Notably, HIV serostatus of the index patient, or their household contacts, was not included in the risk score, owing to the very low prevalence (0•2%) of HIV in Peru. 8 We cannot assume the risk score will perform as well in settings with higher HIV prevalence, because HIV might affect the risk score in unexpected ways. However, in settings where many households affected by tuberculosis are also affected by HIV, the score could still be useful to better prioritise the highest-risk households and ensure that households that could benefit the most from contact investigations are reached.…”