Which diagnostic test to use for Testing and Treatment strategies in low-transmission settings: a secondary analysis of a longitudinal interventional study.

BACKGROUND

The lack of sensitive field tests to diagnose blood stages and hypnozoite carriers prevents Testing and Treatment (TAT) strategies to achieve elimination in low-transmission settings, but recent advances in Polymerase Chain Reaction (PCR) and serology position them as promising tools. This study describes a PCR-based TAT strategy (PCRTAT) implemented in Saint Georges (SGO), French Guiana, and explores alternative strategies (seroTAT and seroPCRTAT) to diagnose and treat carriers.

METHODS

The PALUSTOP cohort study implemented in SGO (September 2017 to December 2018) screened participants for using PCR tests and treated positive cases. Serology was also performed. Passive detection of infection occurred during follow-up. Participants were categorised into overlapping treatment groups based on 2017 PCR and serological results. Strategies were described in terms of participants targeted or missed, primaquine contraindications (pregnancy, G6PD severe or intermediate deficiency), and sociodemographic characteristics.

FINDINGS

In 2017, 1567 inhabitants were included, aged 0-92 years. A total of 90 (6%) were carriers and 390 seropositive (25%). PCRTAT missed 282 seropositive individuals while seroTAT would have missed 21 PCR-positive cases. Primaquine contraindications ranged from 12% to 17% across strategies.

INTERPRETATION

Serology and PCR are promising tools for targeted treatment strategies in low-transmission settings, when field compatible sensitive tests will be available. Both seem necessary to capture blood stages and potential hypnozoite carriers, while avoiding mass treatment. However, high primaquine contraindications rates need consideration for successful elimination.

FUNDING

Supported by European Funds for Regional Development, French Guiana Regional Health Agency, Pan American Health Organization, WHO, French Ministry for Research.