Prevalence and Sequelae of Cryptococcal Antigenemia in Antiretroviral Therapy–Experienced Populations: An Evaluation of Reflex Cryptococcal Antigen Screening in Botswana

Abstract

Background Evidence to inform cryptococcal antigen (CrAg)–screening guidelines among ART-experienced populations is lacking. We performed a study evaluating the utility of reflex CrAg screening in Gaborone, Botswana. Methods CD4 count data were collected from the HIV reference laboratory from 2014–2016. CrAg screening was performed on samples with CD4 ≤100 cells/µL beginning January 2015. The proportion of CD4 counts ≤100 cells/µL was determined and the frequency of repeat CrAg testing described. Analyses ascertained the impact of ART status on CrAg prevalence and outcomes, and whether CrAg titers could be used for risk stratification. Results Overall, 5.6% (3335/59 300) of individuals tested had CD4 ≤100 cells/μL; 2108 samples with CD4 ≤100 cells/μL from 1645 unique patients were CrAg tested. Over half of samples were from ART-experienced individuals: 40.9% (863) on ART and 12.1% (255) defaulters; 22% (463) of CrAg tests were on repeat samples. CrAg prevalence was 4.8% (72/1494; 95% CI, 3.8–6.0%) among outpatients and 21.9% (32/151; 95% CI, 15.3–28.5%) among inpatients. CrAg prevalence rates did not differ by ART status, but 6-month mortality was significantly lower in CrAg-positive individuals on ART at screening. Ten CrAg positives were identified through repeat testing. A CrAg titer cutoff ≥1:80 provided the best discrimination for 6-month survival. Conclusions CrAg-positivity rates in an ART-experienced population were comparable to those seen in ART-naive populations. Repeat screening identified individuals who seroconverted to CrAg positivity and were at risk of cryptococcal disease. CrAg titers ≥1:80 can help identify the individuals at highest risk of death for more intensive management.

Evaluation of a Novel Semiquantitative Cryptococcal Antigen Lateral Flow Assay in Patients with Advanced HIV Disease

“…Accumulating clinical data suggest that quantification of CrAg levels using tests like the CrAgSQ could enable stratification of patients into differentiated diagnostic and treatment pathways. Recent data from CrAg screening programs in Africa have shown that asymptomatic CrAg-positive individuals with CD4 cell counts below 200 cells/l have mortality rates 2-to 3-fold higher than their CrAg-negative counterparts with similar CD4 counts (20,23,24), despite treatment with high-dose oral fluconazole therapy as recommended in WHO guidelines (16). This is likely to be due in part to the presence a To account for the ordered categorical data and assess the degree of disagreement, disagreements were weighted in a linear way: with five categories, cases in adjacent categories were weighted by a factor of 0.75, those with a distance of two categories by a factor of 0.5, those with a distance of three categories by a factor of 0.25, and those with a distance of four categories by a factor of 0. of CNS disease, detectable by LP and CSF evaluation, in approximately one-third of asymptomatic CrAg-positive patients with advanced HIV (18), for whom fluconazole monotherapy is likely to be insufficient to effectively clear infection (25,26).…”

“…Accumulating clinical data suggest that quantification of CrAg levels using tests like the CrAgSQ could enable stratification of patients into differentiated diagnostic and treatment pathways. Recent data from CrAg screening programs in Africa have shown that asymptomatic CrAg-positive individuals with CD4 cell counts below 200 cells/μl have mortality rates 2- to 3-fold higher than their CrAg-negative counterparts with similar CD4 counts ( 20 , 23 , 24 ), despite treatment with high-dose oral fluconazole therapy as recommended in WHO guidelines ( 16 ). This is likely to be due in part to the presence of CNS disease, detectable by LP and CSF evaluation, in approximately one-third of asymptomatic CrAg-positive patients with advanced HIV ( 18 ), for whom fluconazole monotherapy is likely to be insufficient to effectively clear infection ( 25 , 26 ).…”

“…Elevated CrAg titers of >1:160 have been shown to be highly predictive of prevalent CNS disease at the time of CrAg screening (with a sensitivity of 88% and specificity of 82%) in a study from South Africa ( 18 ), with similar findings reported in Ethiopia ( 29 ). Elevated CrAg titers of ≥1:80 or ≥1:160 have also been shown to be strongly associated with increased risk of mortality in CrAg-positive populations ( 19 , 20 ). Our findings that higher CrAgSQ antigen quantification scores are strongly associated with both CNS involvement at baseline in CrAg-positive individuals and higher mortality at 10 weeks add to the already compelling evidence that CrAg titer data could be used to risk stratify CrAg-positive individuals and guide treatment.…”

“…These assessments were performed using the plasma samples from cohort 1 described above plus a collection of stored frozen plasma samples that had previously tested CrAg positive using the IMMY CrAg LFA (cohort 2). Cohort 2 consisted of all plasma samples with positive CrAg tests from a 2015-2016 CrAg screening cohort study performed at BHHRL (20) and from a phase II randomized controlled trial (RCT) evaluating cryptococcal meningitis therapies in Gaborone, Botswana (21).…”

“…Highly sensitive and specific CrAg lateral flow assays (LFAs) ( 10 , 11 ), appropriate for use in laboratories with limited facilities or at the point of care ( 12 ), have markedly facilitated rapid clinical diagnosis of cryptococcal meningitis and also enabled the implementation of CrAg screening programs aimed at detecting and treating early asymptomatic infection in HIV-positive individuals with low CD4 T-cell counts ( 13 – 16 ). Beyond a qualitative (positive/negative) result, higher CrAg titers have been shown to be strongly associated with increased fungal burden and mortality risk in patients with cryptococcal meningitis ( 17 ) and with the presence of central nervous system (CNS) infection and mortality risk among asymptomatic CrAg-positive individuals identified through blood/plasma CrAg screening programs ( 18 – 20 ). Determining CrAg titers may therefore provide important prognostic information, enabling stratification of treatment in individuals with cryptococcal meningitis and identification of CrAg-positive individuals detected through CrAg screening programs who require lumbar puncture (LP) to rule out CNS infection or may benefit from more intensive antifungal therapy.…”