AN EVALUATION OF THE POOLED LOLLI-METHOD RT-qPCR TESTING FOR COVID-19 SURVEILLANCE IN SINGAPORE

Background: Following the success of the Lolli-Method or Lolli-Test as a surveillance method in Germany, the Ministry of Health, Singapore investigated the feasibility of deploying the method as a rostered routine testing in vulnerable individuals such as children, nursing homes and frontline workers; and evaluated the sensitivity and ideal pooling ratio of the Lolli-Method.

Methods: The study was conducted in two phases – the first phase was to assess the operational feasibility of the Lolli-Method. It was held in conjunction with air sampling at a childcare centre with children ages 2 to 6 years old across 40 days. The second phase was to evaluate the sensitivity of the Lolli-Method with different pooling ratios and was conducted in collaboration with the National Centre for Infectious Diseases (NCID) where each pool was spiked with one Lolli swab from a COVID-positive patient. All patients enrolled in this study have their viral load cycle threshold (CT) levels assessed prior to admission via a mid-turbinate oropharyngeal (MTOP) polymerase chain reaction (PCR) swab.

Results: The sensitivity of the pooled Lolli-Test was similar to antigen rapid tests with 100% sensitivity (3/3) in a pooling ratio of 20:1 for patients with viral loads of cycle threshold (CT) levels below 20. For individuals with lower viral loads, the sensitivity of the Lolli-Test was 66.7% (2/3) in a pooling ratio of 20:1 and 100% (2/2) in a smaller pooling ratio of 15:1. The operational feasibility of the Lolli-Test was assessed to be high amongst study participants although students were noted to require some additional assistance from teachers.

Conclusion: The Lolli-Test is an effective surveillance method with adequate sensitivity to detect a COVID-19 infected individual in a pool of up to 20 albeit largely dependent on the viral load. Furthermore, the Lolli-Test also provides a less invasive alternative sample collection method for individuals who cannot tolerate or have contraindications for the regular nasal or oropharyngeal swabs such as young children. More studies should be done to assess the Lolli-Test’s true limit of detection and to evaluate the use of the Lolli-Method in infants and for other respiratory diseases such as influenza.