Validation of clinic-based cryptococcal antigen lateral flow assay screening in HIV-infected adults in South Africa

Paul K. Drain,Sabina Govere,Ting Hong,Meighan Krows,Hilary Thulare,Mahomed-Yunus Moosa,Ingrid V. Bassett,Bernadett I. Gosnell,Carole L. Wallis,Connie Celum

doi:10.1038/s41598-018-37478-7

Abstract

Since rapid cryptococcal antigen lateral flow assays (CrAg LFA) may expedite treatment of HIV-associated cryptococcal infections, we sought to validate clinic-based CrAg LFA testing. Among newly-diagnosed HIV-infected adults in South Africa, a trained nurse performed clinic-based testing of urine, fingerprick capillary and venous whole blood with rapid CrAg LFA (Immy Diagnostics, Norman, USA). We performed matched laboratory-based serum cryptococcal antigen testing with an enzyme immunoassay (EIA). We assessed diagnostic accuracy using EIA as the gold-standard, and performed additional validation testing on serum and among hospitalized adults with cryptococcal meningitis. Among 5,618 participants enrolled, 1,296 were HIV-infected and screened for cryptococcal antigenemia. Overall CrAg prevalence by serum EIA was 3.6% (95% CI 2.0–6.0%) for adults with CD4 < 200 cells/mm3, and 5.7% (95% CI 2.8–10.2%) for adults with CD4 < 100 cells/mm3. Using expanded screening guidelines (CD4 < 200 cells/mm3), CrAg LFA testing of venous whole blood, fingerprick capillary blood, and urine had diagnostic sensitivities of 46% (95% CI 19–75%), 38% (95% CI 14–68%), and 54% (95% CI 25–81%), and specificities of 97%, 97%, and 86%, respectively. When tested on serum samples, CrAg LFA had sensitivity of 93% (95% CI 66–100%) and specificity of 100% (95% CI 88–100%). All venous and fingerprick whole blood CrAg LFA tests were positive among 30 hospitalized adults with cryptococcal meningitis. Two independent readers had strong agreement for all LFA results (p < 0.0001). When performed at the point-of-care by trained nurses, CrAg LFA testing was feasible, had the highest accuracy on serum specimens, and may accelerate treatment of HIV-associated cryptococcal infections.

Highlights

Cryptococcosis is an opportunistic fungal infection that causes approximately 15% of AIDS-related deaths worldwide, the majority of which occur in sub-Saharan Africa[1]
Participants commonly reported clinical symptoms that have been associated with cryptococcal infection or meningitis, including fatigue (47%), headache for >24 hours (30%), weakness in legs (17%), neck stiffness (15%), weakness in arms (14%), difficulty walking (14%), nausea/vomiting (12%), blurry/double vision (7%), confusion (5%), and seizure within last 7 days (1%)
During clinic-based capsular antigens (CrAg) lateral flow assay (LFA) testing, 28 (2.4%), 43 (3.7%), and 123 (10.7%) participants were positive by venous whole blood, fingerprick capillary blood, and urine samples, respectively

Summary

Introduction

Cryptococcosis is an opportunistic fungal infection that causes approximately 15% of AIDS-related deaths worldwide, the majority of which occur in sub-Saharan Africa[1]. In South Africa, cryptococcal infections accounted for approximately 63% of meningitis cases, due in part to the high burden of HIV/AIDS2. Since survival benefit is related to early CrAg screening and prompt initiation of pre-emptive fluconazole therapy, minimizing the time from first clinic visit to testing and subsequent treatment are critical[12]. Survival benefit may be optimized by integrating early CrAg screening and fluconazole pre-emptive therapy while the fungal burden is relatively low prior to the onset of symptomatic meningitis[7,9,12]. The objective was to validate clinic-based rapid CrAg LFA testing on venous whole blood, fingerprick capillary blood, and urine among HIV-infected adults before ART initiation in an ambulatory clinic in South Africa, compared to the gold-standard of an EIA with the same antigens performed on serum

Methods

Results

Conclusion