Use of a rapid digital microfluidics-powered immunoassay for assessing measles and rubella infection and immunity in outbreak settings in the Democratic Republic of the Congo

Abstract

The Democratic Republic of the Congo (DRC) has a high measles incidence despite elimination efforts and has yet to introduce rubella vaccine. We evaluated the performance of a prototype rapid digital microfluidics powered (DMF) enzyme-linked immunoassay (ELISA) assessing measles and rubella infection, by testing for immunoglobulin M (IgM), and immunity from natural infection or vaccine, by testing immunoglobulin G (IgG), in outbreak settings. Field evaluations were conducted during September 2017, in Kinshasa province, DRC. Blood specimens were collected during an outbreak investigation of suspected measles cases and tested for measles and rubella IgM and IgG using the DMF-ELISA in the field. Simultaneously, a household serosurvey for measles and rubella IgG was conducted in a recently confirmed measles outbreak area. DMF-ELISA results were compared with reference ELISA results tested at DRC's National Public Health Laboratory and the US Centers for Disease Control and Prevention. Of 157 suspected measles cases, rubella IgM was detected in 54% while measles IgM was detected in 13%. Measles IgG-positive cases were higher among vaccinated persons (87%) than unvaccinated persons (72%). In the recent measles outbreak area, measles IgG seroprevalence was 93% overall, while rubella seroprevalence was lower for children (77%) than women (98%). Compared with reference ELISA, DMF-ELISA sensitivity and specificity were 82% and 78% for measles IgG; 88% and 89% for measles IgM; 85% and 85% for rubella IgG; and 81% and 83% for rubella IgM, respectively. Rubella infection was detected in more than half of persons meeting the suspected measles case definition during a presumed measles outbreak, suggesting substantial unrecognized rubella incidence, and highlighting the need for rubella vaccine introduction into the national schedule. The performance of the DMF-ELISA suggested that this technology can be used to develop rapid diagnostic tests for measles and rubella.

Fig 1. Serosurvey flowchart illustrating the number of households enumerated and study participants providing specimens.

Fig 2. Performance of DMF-ELISA for assessing 305 specimens for measles IgG (A and B) and 129 specimens for measles IgM (C and D) compared with a reference ELISA.

(A and C) Vertical scatterplot (left) of MR Box 2 signals for specimens determined to be positive or negative for anti-measles IgG (top, n = 305) and IgM (bottom, n = 129) by reference tests. Green and red numbers in the scatterplot represent the number of specimens correctly and incorrectly categorized by the MR Box 2, respectively. (B and D) Receiver Operating Characteristic (ROC) curves with an optimized threshold (X).

Fig 3. Performance of DMF-ELISA for assessing 308 specimens for rubella IgG (A and B) and 127 specimens for rubella IgM (C and D) compared with a reference ELISA.

Vertical scatterplot (left) of MR Box 2 signals for specimens determined to be positive or negative for anti-rubella IgG (top, n = 308) and IgM (bottom, n = 127) by reference tests. Green and red numbers in the scatterplot represent the number of specimens correctly and incorrectly categorized by the MR Box 2, respectively. (B and D) Receiver Operating Characteristic (ROC) curves with an optimized threshold (X).