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Cryptococcal Antigen Screening and Early Antifungal Treatment to Prevent Cryptococcal Meningitis

A Review of the Literature

Kaplan, Jonathan E. MD*; Vallabhaneni, Snigdha MD; Smith, Rachel M. MD; Chideya-Chihota, Sekai MD; Chehab, Joel MPH; Park, Benjamin MD

JAIDS Journal of Acquired Immune Deficiency Syndromes: April 15, 2015 - Volume 68 - Issue - p S331–S339
doi: 10.1097/QAI.0000000000000484
Supplement Article
Free

Background: Screening individuals with AIDS for serum cryptococcal antigen (CrAg), followed by treatment of CrAg positives with antifungals, may prevent cryptococcal meningitis. This review examined data on CrAg screening and treatment in resource-limited settings.

Methods: We searched articles published during 2007–2014 on the effectiveness and cost-effectiveness of CrAg screening and treatment on the outcomes of mortality, morbidity, retention in care, quality of life, and/or prevention of ongoing HIV transmission. We rated overall quality of individual articles, summarized the body of evidence, the expected impact, and cost-effectiveness for each outcome.

Results: We identified 2613 articles. Eight met all inclusion criteria. Five studies addressed mortality and/or morbidity outcomes; all were observational and had small sample sizes; 3 lacked a comparison group. Ratings of study quality ranged from “medium” to “weak,” and the quality of the overall body of evidence for mortality and morbidity outcomes was rated as “fair.” The intervention's expected impact on mortality and morbidity was rated as “moderate.” The 4 cost-effectiveness studies included in the analysis showed that CrAg screening and treatment interventions are highly cost-effective. No studies addressed retention in care, quality of life, or HIV transmission.

Conclusions: Although limited, the body of evidence regarding CrAg screening and treatment suggests that the intervention may have an impact on preventing cryptococcal meningitis and death in persons with AIDS. Additional research is needed to quantify the intervention's effectiveness and identify optimal treatment dosing and implementation best practices.

*HIV Care and Treatment Branch, Division of Global HIV/AIDS, Centers for Disease Control and Prevention, Atlanta, GA; and

Mycotic Diseases Branch, Division of Foodborne-Waterborne and Environmental Diseases, Centers for Disease Control and Prevention, Atlanta, GA.

Correspondence to: Jonathan E. Kaplan, MD, Division of Global HIV/AIDS, Mailstop E-04, Centers for Disease Control and Prevention (CDC), 1600 Clifton Road NE, Atlanta, GA 30333 (e-mail: jxk2@cdc.gov).

Supported by the US President's Emergency Plan for AIDS Relief (PEPFAR) through the Centers for Disease Control and Prevention.

The authors have no conflicts of interest to disclose.

The findings and conclusions in this article are those of the authors and should not be construed to represent the positions of the U.S. Department of State's Office of the US Global AIDS Coordinator and Health Diplomacy, the U.S. Centers for Disease Control and Prevention, or the U.S. Federal Government.

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BACKGROUND

Cryptococcal meningitis (CM), a late and disseminated form of cryptococcal disease, results in substantial morbidity and mortality among HIV-infected individuals.1–5 An article written in 2009 estimated that 720,000 cases of CM occur each year in sub-Saharan Africa, and that mortality due to CM was comparable with that of tuberculosis in countries with large HIV burdens.1 In Southeast Asia, CM is the third most common opportunistic infection among people living with HIV.6–8

Severely immunocompromised HIV-infected individuals with a CD4+ T-lymphocyte (CD4) count <100 cells/μL are at greatest risk for developing CM.9 Treatment of CM requires substantial resources, including hospitalization, intravenous antifungal therapy, access to lumbar punctures, and appropriate monitoring. Because of the severity of disease and limited access to medications and diagnostics, mortality from CM remains high in resource-limited settings (RLS).1,10 Those who do survive often experience long-term severe neurological sequelae because of inadequate control of increased intracranial pressure during the course of their disease.11

Presence of serum cryptococcal antigen (CrAg) is an early biologic marker of disseminated cryptococcal infection in patients with HIV and has been demonstrated up to 234 days before symptoms of meningitis.2 Its presence is highly predictive of development of CM within 1 year,12 and serum CrAg positivity is associated with increased mortality in the first few months of antiretroviral therapy (ART).13 This is believed to be partly due to immune reconstitution inflammatory syndrome in patients with untreated systemic cryptococcal infection.14 For these reasons, screening for serum CrAg among HIV-infected individuals with advanced HIV infection (ie, those with CD4 counts <100 cells/μL) and prompt treatment of CrAg-positive persons with fluconazole, followed by ART, has the potential to prevent progression to CM and to reduce Cryptococcus-associated morbidity and mortality.

In 2011, the WHO issued Rapid Advice with a conditional recommendation that CrAg screening followed by treatment with high-dose fluconazole in persons with advanced HIV infection be considered in settings with a high prevalence of cryptococcal antigenemia.15 At that time, high prevalence was defined as >3%, but more recent analyses have reported that screening may be cost-effective even at a prevalence as low as 0.6%.16–18 Prevalence of serum CrAg in persons with advanced HIV infection ranges between 1% and 16% in sub-Saharan African and Southeast Asian countries.9,12–14,17,19–26 Many countries have expressed interest in CrAg screening and early treatment; a few, such as South Africa, Rwanda, and Mozambique, are already implementing such programs. However, prevention of disseminated cryptococcal disease is one among many aspects of HIV care that countries must consider; in the setting of competing demands and limited resources, countries have to prioritize their HIV care and support activities. The following review of the evidence aims to help guide countries that are considering implementation of a cryptococcal screening program, as they attempt to prioritize their HIV care and support activities.

The objective of this review was to examine existing data on CrAg screening and treatment in RLS. We defined the intervention of interest as screening of HIV-infected persons with advanced immunosuppression for CrAg, and treating asymptomatic CrAg-positive persons with fluconazole to prevent CM. In this review, we assessed the quality of published studies and the likely impact of the intervention on the following clinical outcomes: (1) mortality, (2) morbidity, (3) retention in HIV care, (4) quality of life, and (5) prevention of ongoing HIV transmission. Additionally, we evaluated data on cost-effectiveness of cryptococcal screening and treatment. This article is one of the 12 articles in this supplement evaluating care and support interventions offered through the US President's Emergency Plan for AIDS Relief (PEPFAR) in RLS.

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METHODS

We conducted a literature search of 6 medical literature databases—Medline, Embase, Global Health, CINAHL, SOCA, and African Index Medicus (AIM)—to identify articles relevant to the cryptococcal screen and treat intervention from January 2007 to May 2014. A detailed description of the search terms applied and the geographic filters used can be found in the introductory article in this Supplement.27 The additional search terms specifically related to cryptococcal screening and treatment are shown in Table 1.

TABLE 1

TABLE 1

Search outputs (titles and abstracts) were reviewed by the authors to identify potentially relevant studies. Articles that appeared to contain data relevant to the intervention and to one or more of the outcomes of interest (“eligible” studies) were retrieved and read in their entirety. Those that in fact satisfied criteria for inclusion, that is, they (1) studied persons with HIV infection, (2) were conducted in resource-limited settings, (3) described screening of HIV-infected persons with advanced immunosuppression for CrAg and treating asymptomatic CrAg-positive persons with fluconazole to prevent CM, and (4) reported at least 1 of the 5 outcomes of interest (mortality, morbidity, retention in HIV care, quality of life, or prevention of ongoing HIV transmission) or costing or cost effectiveness, “included studies,” were abstracted and summarized on the basis of study design (eg, randomized control trial, cohort study), comparison group(s), number of participants, and assessment of impact on the outcome(s) of interest (expressed as hazard ratios, odds ratios, or relative risk and the respective 95% confidence intervals if available). An assessment of the quality of each study was made on the basis of study design, number of participants, and internal and external validity; quality was rated as “strong,” “medium,” or “weak.” Cost-effectiveness studies were assessed as follows: Level 1 (full economic evaluation that includes cost-effectiveness analysis, cost-utility analysis, or cost–benefit analysis); Level 2 (partial economic evaluations, ie, cost analyses, cost–description studies, cost–outcome descriptions); or Level 3 (randomized trials and studies reporting more limited information, such as estimates of resource use or costs associated with intervention(s) and comparator(s)). More details of the assessment of quality are described in the introductory article in this Supplement.27

Because of the heterogeneity of study populations, study methods, settings, and outcomes, we did not perform quantitative synthesis of study results overall. However, studies were grouped together by the outcome(s) they addressed, and the quality of the body of evidence pertaining to each outcome was rated as good, fair, or poor based on criteria agreed on a priori and described in the introductory article. Finally, the assessment of expected impact on each outcome was rated as high, moderate, low, or uncertain (criteria described in the introductory article in this Supplement).27

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RESULTS

Of 2613 manuscripts and conference abstracts identified using the search terms, 19 contained information that seemed to be related to the CrAg screen and treat intervention for at least 1 of the 5 outcomes of interest (Fig. 1). Of these 19 articles, 8 contained information that satisfied the criteria for inclusion. Of these 8, one study addressed mortality, morbidity, and cost-effectiveness; 4 additional studies focused on mortality, morbidity, or both; and 3 articles described findings from cost-effectiveness modeling. None of the 8 studies assessed retention in HIV care, quality of life, or prevention of ongoing HIV transmission as outcome measures. Table 2 summarizes the study design, sample size, findings, and the quality of evidence rating of the 8 articles meeting final inclusion criteria.

FIGURE 1

FIGURE 1

TABLE 2-a

TABLE 2-a

TABLE 2-b

TABLE 2-b

All 5 of the studies addressing mortality or morbidity of the intervention were observational (nonrandomized) studies. Three of them lacked comparison groups; sample sizes were small with 4 of the 5 studies evaluating less than 35 participants each.

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Clinical Outcomes, Quality of Evidence, and Cost-Effectiveness

Mortality

Five observational studies examined the impact of the CrAg screen and treat strategy on mortality. Meya et alcryptococcal antigen screening to prevent deaths among HIV-infected persons with a CD4+ cell count < or = 100 cells/microL who start HIV therapy in resource-limited settings. Clin Infect Dis. 2010;51:448–455.','400');" onMouseOut="javascript:ImageWrapperControl_ImageMouseOut();">20 found that among CrAg-positive HIV-infected persons without a history of CM, treatment with fluconazole was associated with higher odds of survival (OR: 34.6, 95% CI: 1.7 to 703) compared with those not treated with fluconazole in a multivariate logistic regression model. Among the 26 patients with a positive CrAg and a CD4 count <100 cells/μL, 21 were treated with fluconazole and ART and 5 received ART alone. Six of the 21 (29%) fluconazole-treated patients died, compared with 5/5 (100%) of those who were treated with ART alone. In contrast, an observational cohort study of 782 HIV-positive individuals conducted in Kenya found no mortality benefit with the CrAg screen and treat strategy compared with a historical cohort of similar patients who initiated ART before the CrAg screen and treat protocol was in place (HR = 1.1; 95% CI: 0.9 to 1.3).26 However, only 52% of persons eligible for the intervention actually received the intervention.

Three other small observational studies found that asymptomatic CrAg-positive persons who were treated with fluconazole had mortality rates of 3.3% (1/30 participants at 6 months)28 0% (0/8 participants at 1 year),9 and 20% (2/10 participants at 12 weeks),19 respectively, but none of these studies included a comparison group.

The overall quality of evidence of studies examining mortality was determined to be “fair,” and the expected impact of the CrAg screen and treat intervention on mortality was assessed to be “moderate” (Table 3).

TABLE 3

TABLE 3

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Morbidity

Two studies from Meyacryptococcal antigen screening to prevent deaths among HIV-infected persons with a CD4+ cell count < or = 100 cells/microL who start HIV therapy in resource-limited settings. Clin Infect Dis. 2010;51:448–455.','400');" onMouseOut="javascript:ImageWrapperControl_ImageMouseOut();">20 and Chim28 assessed the impact of the CrAg screen and treat strategy on morbidity, specifically the prevention of CM. Meya et alcryptococcal antigen screening to prevent deaths among HIV-infected persons with a CD4+ cell count < or = 100 cells/microL who start HIV therapy in resource-limited settings. Clin Infect Dis. 2010;51:448–455.','400');" onMouseOut="javascript:ImageWrapperControl_ImageMouseOut();">20 reported that 3 of 21 (14%) CrAg-positive fluconazole-treated patients developed CM, compared with 2 of 5 (40%) patients who did not receive fluconazole. The small sample size prevented the investigators from determining if this difference was statistically significant. Chim et al28 found that 1 of 22 patients (4.5%) who were serum CrAg-positive and treated with 400 mg of fluconazole daily for 8 weeks followed by 200 mg of fluconazole daily, developed incident CM within 6 months after fluconazole treatment was initiated. Although there was no comparison group in this study, the authors compared this result to previous studies, which reported that up to 30% of untreated CrAg-positive patients develop CM.9,12 The overall quality of evidence of studies examining morbidity was determined to be “fair” and the expected impact of the CrAg screen and treat on morbidity was assessed to be “moderate” (Table 3).

Comparisons between the studies assessing mortality and/or morbidity are complicated by the heterogeneity of the studies, including study design and variable fluconazole doses, treatment durations, and follow-up periods. Although all 5 studies examining morbidity and/or mortality used fluconazole for treatment, regimen dosages and schedules differed. For one study, the fluconazole dosage used was not disclosed.9 Dosages ranged from 200 to 400 mg per day administered for 2 or more weeks, depending on the context; these short course low-dose regimens may have adversely impacted morbidity and mortality outcomes.

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Cost-Effectiveness

Four studies addressed the cost-effectiveness of the screen and treat approach, 2 in SSA and 2 in Southeast Asia (Fig. 1, Table 4). All 4 studies found the intervention to be highly cost-effective. Smith et al17 found that in Vietnam, where the prevalence of CrAg positivity among HIV-infected persons with advanced immunosuppression was 2%–6%, a cryptococcal screening program would cost less than $190 per life-year gained (LYG). The cost-effectiveness of a CrAg screen and treat strategy was comparable with that of pneumocystis pneumonia prophylaxis, which is widely accepted as a highly cost-effective intervention. In Uganda, Meya et alcryptococcal antigen screening to prevent deaths among HIV-infected persons with a CD4+ cell count < or = 100 cells/microL who start HIV therapy in resource-limited settings. Clin Infect Dis. 2010;51:448–455.','400');" onMouseOut="javascript:ImageWrapperControl_ImageMouseOut();">20 calculated that the number needed to test and treat with CrAg screening and fluconazole to prevent 1 CM case was 11.3 persons, and the number needed to treat to save 1 life was 15.9. They also found the intervention to be highly cost-effective with a cost of $21 per disability-adjusted life year averted. In Cambodia, the CrAg screen and treat intervention of HIV-infected persons with CD4 count <100 cells/μL was found to be more cost-effective [incremental cost-effectiveness ratio (ICER)/LYG was $180] than providing fluconazole prophylaxis for all HIV-infected persons with a CD4 count <100 cells/μL (ICER/LYG = $511).18 Finally, Jarvis et al16 reported that in South Africa, screening HIV-infected persons with CD4 <100 cells/μL and treatment of CrAg-positive persons (mean cost per person-year was $51) was more cost-effective than both the standard protocol of conducting no screening ($207 per person-year) and giving fluconazole prophylaxis to all persons with a CD4 <100 cells/μL ($582 per person/year). Even with CrAg prevalence as low as 0.6%, this intervention was found to be cost-effective.

TABLE 4

TABLE 4

It is important to note that the cost-effectiveness studies used effectiveness data from the above-mentioned small observational studies. Additionally, the methodology used in each study differed substantially, including which costs were included, cost-effectiveness metrics used, and which strategies were compared. Despite these limitations, the overall quality of the cost-effectiveness evidence was assessed as very good based on consistent results from multiple well-designed well-conducted studies in representative populations.

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DISCUSSION

Our review identified 8 articles published from 2007 through 2014 that reported data on either the clinical impact or cost-effectiveness of cryptococcal screen and treat strategies in resource-limited settings. Although limited, these data suggest potential benefit of the CrAg screen and treat strategy in preventing CM and death in persons with AIDS. Available data also indicate that the CrAg screen and treat approach is more cost-effective than no screening and more cost-effective than routine fluconazole prophylaxis of all HIV-infected persons with low CD4 counts in RLS. As countries become more successful in identifying HIV-infected persons and enrolling them in HIV care, the average CD4 count at initiation is likely to increase, and fewer persons will be at risk for CM. However, late presentation to care (CD4 <200 cells/μL or <100 cells/μL) is currently very common around the world and will likely remain a challenge in the near future. Thus, it is likely that large numbers of individuals will continue to present with advanced HIV infection and will therefore be at risk for development of cryptococcal disease.

Recent advances in diagnostics for detecting CrAg may make screening even more cost-effective and easy to implement. Latex agglutination (LA) testing for detection of CrAg has been in use for many years. LA, although sensitive, specific, and relatively fast (10–30 minutes for result), requires laboratory infrastructure, including reagents and refrigeration, and technical expertise to interpret results. LA is also intermediately expensive, with each test costing approximately $10; all but one of the CE studies17 included in this review used LA cost assumptions to determine cost-effectiveness. The newly developed lateral flow assay (LFA) for CrAg (Immuno-Mycologics, Inc., Norman, OK) has several advantages over LA. The LFA is an immunochromatographic dipstick assay, which is highly sensitive and specific, requires far less laboratory infrastructure and training than earlier assays, takes 10 minutes to perform, is stable at room temperature, and is relatively inexpensive (approximately US$2/test).29 The CrAg LFA was approved by the FDA in 2011 for use on serum and CSF and was also Conformité Européene (CE)–marked in Europe for serum, plasma, whole blood (venous and finger stick), and CSF. These advantages of the LFA in price and ease of use make screening for CrAg potentially scalable in laboratories and for point-of-care use in RLS with a high burden of CM.

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Research Gaps

Randomized controlled trials comparing clinical outcomes with screening and treatment to those without screening or treatment (or current practice) would provide the highest quality of evidence on effectiveness of this intervention. However, conducting such a trial could be ethically challenging in light of the WHO Rapid Advice on CrAg screening and treatment and existing data. Indeed, several countries, including South Africa, Rwanda, Mozambique, Zimbabwe, Uganda, Namibia, and Lesotho, have, or are in the process of developing national guidelines for CrAg screen and treat interventions, making a randomized controlled trial at the patient level impractical and potentially unethical. One ongoing study in Uganda will hopefully shed more light on the effectiveness of this strategy (http://clinicaltrials.gov/ct2/show/NCT), Rather than randomizing at the individual patient level, this trial uses a “stepped wedge” strategy to introduce the screen and treat intervention at clinic sites randomized to initiate the intervention at different times. The study will compare morbidity and mortality pre- and post-intervention. Future research should also examine the optimal dosing and duration of fluconazole treatment for CrAg-positive persons and ART-start time for those who have asymptomatic antigenemia. Many questions remain unanswered about the effectiveness, and cost-effectiveness, of cryptococcal screening and treatment, particularly regarding patient CD4 counts and CrAg testing method and setting (eg, LA, LFA, laboratory-based, point-of-care testing).

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Programmatic Considerations for Implementation

CrAg screening and treatment is currently being implemented in several countries by integrating screening into existing HIV care and support activities. This literature review has yielded valuable information regarding considerations for implementing “screen and treat” programs in resource-limited countries. The “screen and treat” approach requires the provision of several key services, including CrAg screening of ART-naive HIV-infected persons with low CD4 counts, thorough evaluation for symptoms of CM, timely treatment of asymptomatic CrAg-positive persons with fluconazole, adherence counseling, and appropriate patient monitoring and follow-up. Countries considering implementation of a screen and treat program should conduct an initial assessment of the current situation in country. Such an assessment might include an evaluation of disease burden (both CM and prevalence of CrAg positivity in persons with low CD4 counts), laboratory and diagnostic capacity (including human resources), access to antifungal medications, and stakeholder interest in implementing the intervention. Countries deciding to implement the intervention would need to develop a strategy to develop/adapt national guidelines to include the recommendations for cryptococcal screening, diagnostics, and treatment based on the 2011 WHO Rapid Advice guidelines. After securing access to CrAg tests, such as the LFA, countries need to expand access to antifungal medicines. Decisions about the best implementation strategy (reflexive, laboratory-based testing or provider initiated screening; centralized testing/point-of-care testing) for effective integration of the intervention into other HIV-care services need to be made, and training of appropriate laboratory and clinical staff to carry out the program should be conducted. Finally, countries should consider incorporating routine program monitoring and evaluation to ensure that goals are met and iterative improvement can be made.

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Limitations

One of the 2 observational studies with comparison groupscryptococcal antigen screening to prevent deaths among HIV-infected persons with a CD4+ cell count < or = 100 cells/microL who start HIV therapy in resource-limited settings. Clin Infect Dis. 2010;51:448–455.','400');" onMouseOut="javascript:ImageWrapperControl_ImageMouseOut();">20 suggested strong benefit of the intervention, but patients were not randomized and the numbers were small. The other observational study26 did not demonstrate benefit of the screen and treat approach but was hampered by suboptimal implementation of the intervention. Assessment of efficacy is also complicated by the use of different doses and duration of fluconazole therapy across studies. WHO recommends fluconazole 800 mg/d for 2 weeks, followed by 400 mg/d for 8 weeks, followed by 200 mg/d maintenance.15 Because all of the studies were observational in nature, treatment of CrAg-positive persons was left to the discretion of the patient's provider. The WHO-recommended regimen was used in only one of the 4 studies examining mortality as an outcome for which this information was available. The intervention may have been shown to be more effective than current evidence indicates if high-dose fluconazole had been used in these studies. Most of the cost-effectiveness studies required the use of modeling and educated assumptions because robust effectiveness data are lacking.

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CONCLUSIONS

Although limited, the body of evidence about cryptococcal antigen screening and early treatment with fluconazole suggests that the intervention is likely to have a significant impact on preventing CM and death in persons with AIDS if implemented well. This summary of evidence may be useful to national HIV/AIDS programs considering implementing cryptococcal antigen screen and treat programs and may provide background for the design of future studies of cryptococcal screen and treat effectiveness. Continued research is needed to quantify the effectiveness of screening, examine optimal fluconazole dosing and duration for treatment of isolated cryptococcal antigenemia, and identify best practices for implementation of a screening program in various settings.

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ACKNOWLEDGMENTS

The authors acknowledge Gail Bang and Emily Weyant for conducting the literature searches and Jean Michel Tchuenche for evaluation of the cost-effectiveness studies.

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Keywords:

cryptococcal antigen; screening; cryptococcal meningitis

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