Multicountry Validation of SAMBA - A Novel Molecular Point-of-Care Test for HIV-1 Detection in Resource-Limited Setting

Point-of-care viral load tests to detect high HIV viral load in people living with HIV/AIDS attending health facilities

BACKGROUND

Viral load (VL) testing in people living with HIV (PLHIV) helps to monitor antiretroviral therapy (ART). VL is still largely tested using central laboratory-based platforms, which have long test turnaround times and involve sophisticated equipment. VL tests with point-of-care (POC) platforms capable of being used near the patient are potentially easy to use, give quick results, are cost-effective, and could replace central or reference VL testing platforms.

OBJECTIVES

To estimate the diagnostic accuracy of POC tests to detect high viral load levels in PLHIV attending healthcare facilities.

SEARCH METHODS

We searched eight electronic databases using standard, extensive Cochrane search methods, and did not use any language, document type, or publication status limitations. We also searched the reference lists of included studies and relevant systematic reviews, and consulted an expert in the field from the World Health Organization (WHO) HIV Department for potentially relevant studies. The latest search was 23 November 2020.

SELECTION CRITERIA

We included any primary study that compared the results of a VL test with a POC platform to that of a central laboratory-based reference test to detect high viral load in PLHIV on HIV/AIDS care or follow-up. We included all forms of POC tests for VL as defined by study authors, regardless of the healthcare facility in which the test was conducted. We excluded diagnostic case-control studies with healthy controls and studies that did not provide sufficient data to create the 2 × 2 tables to calculate sensitivity and specificity. We did not limit our study inclusion to age, gender, or geographical setting.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened the titles, abstracts, and full texts of the search results to identify eligible articles. They also independently extracted data using a standardized data extraction form and conducted risk of bias assessment using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool. Using participants as the unit of analysis, we fitted simplified univariable models for sensitivity and specificity separately, employing a random-effects model to estimate the summary sensitivity and specificity at the current and commonly reported World Health Organization (WHO) threshold (≥ 1000 copies/mL). The bivariate models did not converge to give a model estimate.

MAIN RESULTS

We identified 18 studies (24 evaluations, 10,034 participants) defining high viral loads at main thresholds ≥ 1000 copies/mL (n = 20), ≥ 5000 copies/mL (n = 1), and ≥ 40 copies/mL (n = 3). All evaluations were done on samples from PLHIV retrieved from routine HIV/AIDS care centres or health facilities. For clinical applicability, we included 14 studies (20 evaluations, 8659 participants) assessing high viral load at the clinical threshold of ≥ 1000 copies/mL in the meta-analyses. Of these, sub-Saharan Africa, Europe, and Asia contributed 16, three, and one evaluation respectively. All included participants were on ART in only nine evaluations; in the other 11 evaluations the proportion of participants on ART was either partial or not clearly stated. Thirteen evaluations included adults only (n = 13), five mixed populations of adults and children, whilst in the remaining two the age of included populations was not clearly stated. The majority of evaluations included commercially available tests (n = 18). Ten evaluations were POC VL tests conducted near the patient in a peripheral or onsite laboratory, whilst the other 10 were evaluations of POC VL tests in a central or reference laboratory setting. The test types evaluated as POC VL tests included Xpert HIV-1 Viral Load test (n = 8), SAMBA HIV-1 Semi-Q Test (n = 9), Alere Q NAT prototype assay for HIV-1 (n = 2) and m-PIMA HIV-1/2 Viral Load test (n = 1). The majority of evaluations (n = 17) used plasma samples, whilst the rest (n = 3) utilized whole blood samples. Pooled sensitivity (95% confidence interval (CI)) of POC VL at a threshold of ≥ 1000 copies/mL was 96.6% (94.8 to 97.8) (20 evaluations, 2522 participants), and pooled specificity (95% CI) was 95.7% (90.8 to 98.0) (20 evaluations, 6137 participants). Median prevalence for high viral load (≥ 1000 copies/mL) (n = 20) was 33.4% (range 6.9% to 88.5%). Limitations The risk of bias was mostly assessed as unclear across the four domains due to incomplete reporting.

AUTHORS' CONCLUSIONS

We found POC VL to have high sensitivity and high specificity for the diagnosis of high HIV viral load in PLHIV attending healthcare facilities at a clinical threshold of ≥ 1000 copies/mL.

Point-of-care tests detecting HIV nucleic acids for diagnosis of HIV-1 or HIV-2 infection in infants and children aged 18 months or less

BACKGROUND

The standard method of diagnosing HIV in infants and children less than 18 months is with a nucleic acid amplification test reverse transcriptase polymerase chain reaction test (NAT RT-PCR) detecting viral ribonucleic acid (RNA). Laboratory testing using the RT-PCR platform for HIV infection is limited by poor access, logistical support, and delays in relaying test results and initiating therapy in low-resource settings. The use of rapid diagnostic tests at or near the point-of-care (POC) can increase access to early diagnosis of HIV infection in infants and children less than 18 months of age and timely initiation of antiretroviral therapy (ART).

OBJECTIVES

To summarize the diagnostic accuracy of point-of-care nucleic acid-based testing (POC NAT) to detect HIV-1/HIV-2 infection in infants and children aged 18 months or less exposed to HIV infection.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (until 2 February 2021), MEDLINE and Embase (until 1 February 2021), and LILACS and Web of Science (until 2 February 2021) with no language or publication status restriction. We also searched conference websites and clinical trial registries, tracked reference lists of included studies and relevant systematic reviews, and consulted experts for potentially eligible studies.

SELECTION CRITERIA

We defined POC tests as rapid diagnostic tests conducted at or near the patient site. We included any primary study that compared the results of a POC NAT to a reference standard of laboratory NAT RT-PCR or total nucleic acid testing to detect the presence or absence of HIV infection denoted by HIV viral nucleic acids in infants and children aged 18 months or less who were exposed to HIV-1/HIV-2 infection. We included cross-sectional, prospective, and retrospective study designs and those that provided sufficient data to create the 2 × 2 table to calculate sensitivity and specificity. We excluded diagnostic case control studies with healthy controls.

DATA COLLECTION AND ANALYSIS

We extracted information on study characteristics using a pretested standardized data extraction form. We used the QUADAS-2 (Quality Assessment of Diagnostic Accuracy Studies) tool to assess the risk of bias and applicability concerns of the included studies. Two review authors independently selected and assessed the included studies, resolving any disagreements by consensus. The unit of analysis was the participant. We first conducted preliminary exploratory analyses by plotting estimates of sensitivity and specificity from each study on forest plots and in receiver operating characteristic (ROC) space. For the overall meta-analyses, we pooled estimates of sensitivity and specificity using the bivariate meta-analysis model at a common threshold (presence or absence of infection).

MAIN RESULTS

We identified a total of 12 studies (15 evaluations, 15,120 participants). All studies were conducted in sub-Saharan Africa. The ages of included infants and children in the evaluations were as follows: at birth (n = 6), ≤ 12 months (n = 3), ≤ 18 months (n = 5), and ≤ 24 months (n = 1). Ten evaluations were field evaluations of the POC NAT test at the point of care, and five were laboratory evaluations of the POC NAT tests.The POC NAT tests evaluated included Alere q HIV-1/2 Detect qualitative test (recently renamed m-PIMA q HIV-1/2 Detect qualitative test) (n = 6), Xpert HIV-1 qualitative test (n = 6), and SAMBA HIV-1 qualitative test (n = 3). POC NAT pooled sensitivity and specificity (95% confidence interval (CI)) against laboratory reference standard tests were 98.6% (96.1 to 99.5) (15 evaluations, 1728 participants) and 99.9% (99.7 to 99.9) (15 evaluations, 13,392 participants) in infants and children ≤ 18 months. Risk of bias in the included studies was mostly low or unclear due to poor reporting. Five evaluations had some concerns for applicability for the index test, as they were POC tests evaluated in a laboratory setting, but there was no difference detected between settings in sensitivity (-1.3% (95% CI -4.1 to 1.5)); and specificity results were similar.

AUTHORS' CONCLUSIONS

For the diagnosis of HIV-1/HIV-2 infection, we found the sensitivity and specificity of POC NAT tests to be high in infants and children aged 18 months or less who were exposed to HIV infection.

Viral load care of HIV-1 infected children and adolescents: A longitudinal study in rural Zimbabwe

INTRODUCTION

Maintaining virologic suppression of children and adolescents on ART in rural communities in sub-Saharan Africa is challenging. We explored switching drug regimens to protease inhibitor (PI) based treatment and reducing nevirapine and zidovudine use in a differentiated community service delivery model in rural Zimbabwe.

METHODS

From 2016 through 2018, we followed 306 children and adolescents on ART in Hurungwe, Zimbabwe at Chidamoyo Christian Hospital, which provides compact ART regimens at 8 dispersed rural community outreach sites. Viral load testing was performed (2016) by Roche and at follow-up (2018) by a point of care viral load assay. Virologic failure was defined as viral load ≥1,000 copies/ml. A logistic regression model which included demographics, treatment regimens and caregiver's characteristics was used to assess risks for virologic failure and loss to follow-up (LTFU).

RESULTS

At baseline in 2016, 296 of 306 children and adolescents (97%) were on first-line ART, and only 10 were receiving a PI-based regimen. The median age was 12 years (IQR 8-15) and 55% were female. Two hundred and nine (68%) had viral load suppression (<1,000 copies/ml) and 97(32%) were unsuppressed (viral load ≥1000). At follow-up in 2018, 42/306 (14%) were either transferred 23 (7%) or LTFU 17 (6%) and 2 had died. In 2018, of the 264 retained in care, 107/264 (41%), had been switched to second-line, ritonavir-boosted PI with abacavir as a new nucleotide analog reverse transcriptase inhibitor (NRTI). Overall viral load suppression increased from 68% in 2016 to 81% in 2018 (P<0.001).

CONCLUSION

Viral load testing, and switching to second-line, ritonavir-boosted PI with abacavir significantly increased virologic suppression among HIV-infected children and adolescents in rural Zimbabwe.

Performance Evaluation of the SAMBA II SARS-CoV-2 Test for Point-of-Care Detection of SARS-CoV-2

Nucleic acid amplification for the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA in respiratory samples is the standard method for diagnosis. The majority of this testing is centralized and therefore has turnaround times of several days. Point-of-care (POC) testing with rapid turnaround times would allow more effective triage in settings where patient management and infection control decisions need to be made rapidly. The inclusivity and specificity of the Simple AMplification-Based Assay (SAMBA) II SARS-CoV-2 test were determined by both in silico analyses of the primers and probes and wet testing. The SAMBA II SARS-CoV-2 test was evaluated for performance characteristics. Clinical performance was evaluated in residual combined throat/nose swabs and compared to that of the Public Health England real-time PCR assay targeting the RdRp gene. The SAMBA II SARS-CoV-2 test has an analytical sensitivity of 250 copies/ml for detecting two regions of the genome (open reading frame 1ab [ORF1ab] and nucleocapsid protein [N]). The clinical performance was evaluated in 172 residual combined nose/throat swabs provided by the Clinical Microbiology and Public Health Laboratory, Addenbrooke's Hospital, Cambridge (CMPHL), which showed an estimated positive percent agreement of 98.9% (95% confidence interval [CI], 93.83 to 99.97) and negative percent agreement of 96.4% (95% CI, 89.92 to 99.26) compared to testing by the CMPHL. The data show that the SAMBA II SARS-CoV-2 test performs equivalently to the centralized testing methods, but with a shorter turnaround time of 86 to 101 min. Point-of-care tests such as SAMBA should enable rapid patient management and effective implementation of infection control measures.

Providing competent, comprehensive and inclusive sexual health services for men who have sex with men in low- and middle-income countries: a scoping review

Although men who have sex with men (MSM) are disproportionately affected by HIV and other sexually transmissible infections, sexual health services for MSM in low- and middle-income countries (LMIC) remain under-resourced and are poorly understood. A scoping review of literature on MSM sexual health in LMIC was conducted in order to identify key clinical services and gaps in knowledge. Three databases were searched, in addition to hand-reviewing key journals and bulletins, to identify literature with a focus on MSM sexual health. Key services related to providing care to MSM in LMIC that emerged from our review are described. These services include creation of safe and confidential clinic environments, HIV testing services, behavioural interventions, HIV pre-exposure prophylaxis (PrEP), rapid antiretroviral therapy (ART) initiation and STI services. Compared with high-income settings, major differences in LMIC include lack of diagnostic technology, unfavourable legal environments and lack of funding for MSM health. Innovative approaches to healthcare delivery, such as harnessing mobile technology, self-testing and crowdsourcing interventions, can improve health services among MSM in LMIC. There are gaps in the evidence about how best to provide sexual health services for MSM in LMIC settings. Implementation research and scale-up of existing biomedical and behavioural interventions, such as HIV/STI testing services, PrEP and early antiretroviral initiation are urgently needed in LMIC.

Point of Care Nucleic Acid Testing for SARS-CoV-2 in Hospitalized Patients: A Clinical Validation Trial and Implementation Study

There is an urgent need for rapid SARS-CoV-2 testing in hospitals to limit nosocomial spread. We report an evaluation of point of care (POC) nucleic acid amplification testing (NAAT) in 149 participants with parallel combined nasal and throat swabbing for POC versus standard lab RT-PCR testing. Median time to result is 2.6 (IQR 2.3-4.8) versus 26.4 h (IQR 21.4-31.4, p < 0.001), with 32 (21.5%) positive and 117 (78.5%) negative. Cohen's κ correlation between tests is 0.96 (95% CI 0.91-1.00). When comparing nearly 1,000 tests pre- and post-implementation, the median time to definitive bed placement from admission is 23.4 (8.6-41.9) versus 17.1 h (9.0-28.8), p = 0.02. Mean length of stay on COVID-19 "holding" wards is 58.5 versus 29.9 h (p < 0.001). POC testing increases isolation room availability, avoids bed closures, allows discharge to care homes, and expedites access to hospital procedures. POC testing could mitigate the impact of COVID-19 on hospital systems.

Vertical transmission of HIV among pregnant women who initially had false-negative rapid HIV tests in four South African antenatal clinics

INTRODUCTION

There is a risk of mother-to-child transmission of HIV (MTCT) during pregnancy and breastfeeding. The aim of this study was to assess vertical transmission of HIV among pregnant women who initially had false-negative rapid HIV tests in South African antenatal care (ANC) clinics.

METHODS

Pregnant participants were enrolled in a diagnostic study that used nucleic acid amplification testing (NAAT) to screen for early HIV infection among individuals who tested negative on rapid HIV tests used at the point-of-care (POC) facilities. Participants were enrolled from four ANC clinics in the Tshwane district of South Africa. All NAAT-positive participants were recalled to the clinics for further management. Vertical transmission was assessed among exposed infants whose HIV polymerase chain reaction (PCR) results were available.

RESULTS

This study enrolled 8208 pregnant participants who tested negative on rapid HIV tests between 2013 and 2016. Their median age was 26 years (interquartile range [IQR]: 23-30). NAAT detected HIV infections in 0.6% (n = 49; 95% confidence interval {CI}: 0.5-0.8) of all study participants. The distribution of these infections among the four clinics ranged from 0.3%- 1.1%, but this was not statistically significant (p = 0.07). Forty-seven participants (95.9%) were successfully recalled and referred for antiretroviral treatment initiation as part of prevention of MTCT (PMTCT). Most women with newly diagnosed HIV infection presented for the first ANC visit in the second (61.9%, n = 26) and third (31.0%, n = 13) trimesters. HIV PCR results were available for thirty-two infants, three of whom tested positive (9.4%; 95% CI: 1.98-25.02).

CONCLUSIONS

This study showed that supplemental HIV testing for pregnant women led to earlier linkage to the PMTCT programme. Inaccurate diagnosis of HIV infection at ANC clinics is likely to undermine the efforts of eliminating MTCT particularly in HIV-endemic settings.

Challenges of HIV diagnosis and management in the context of pre-exposure prophylaxis (PrEP), post-exposure prophylaxis (PEP), test and start and acute HIV infection: a scoping review

INTRODUCTION

Knowledge of HIV status relies on accurate HIV testing, and is the first step towards access to HIV treatment and prevention programmes. Globally, HIV-status unawareness represents a significant challenge for achieving zero new HIV infections and deaths. In order to enhance knowledge of HIV status, the World Health Organisation (WHO) recommends a testing strategy that includes the use of HIV-specific antibody point-of-care tests (POCT). These POCTs do not detect acute HIV infection, the stage of disease when viral load is highest but HIV antibodies are undetectable. Complicating things further, in the presence of antiretroviral therapy (ART) for pre-exposure prophylaxis (PrEP) or post-exposure prophylaxis (PEP), other currently available testing technologies, such as viral load detection for diagnosis of acute HIV infection, may yield false-negative results. In this scoping review, we evaluate the evidence and discuss alternative HIV testing algorithms that may mitigate diagnostic dilemmas in the setting of increased utilization of ART for immediate treatment and prevention of HIV infection.

DISCUSSION

Missed acute HIV infection prevents people living with HIV (PLHIV) from accessing early treatment, increases likelihood of onward transmission, and allows for inappropriate initiation or continuation of PrEP, which may result in HIV drug resistance. While immediate ART is recommended for all PLHIV, studies have shown that starting ART in the setting of acute HIV infection may result in a delayed or complete absence of development of HIV-specific antibodies, posing a diagnostic challenge that is particularly pertinent to resource-limited, high HIV burden settings where HIV-antibody POCTs are standard of care. Similarly, ART used as PrEP or PEP may supress HIV RNA viral load, complicating current HIV testing algorithms in resource-wealthy settings where viral detection is included. As rollout of PrEP continues, HIV testing algorithms may need to be modified.

CONCLUSIONS

With increasing use of PrEP and ART in acute infection we anticipate diagnostic challenges using currently available HIV testing strategies. Research and surveillance are needed to determine the most appropriate assays and optimal testing algorithms that are accurate, affordable and sustainable.

HIV DNA Measurement and Improved Detection of HIV Infection Among Men Who Have Sex with Men: A Strategic Implication

Rapid test (RT) is the principal screening method in the HIV control practice. However, this method may lead to inaccurate detection, primarily due to the more than 4 weeks of window phase. In the present study, we performed a HIV DNA screening method to show its application prospects in men who have sex with men (MSM). From July 2017 to April 2018, we recruited 1,301 MSM from Beijing who were not previously diagnosed as HIV positive. Both HIV DNA detection and RT were performed. In total, 141 and 135 HIV-positive results were detected by DNA detection and RT, respectively. By repetitive and confirmative tests (Western blot), we verified that DNA detection detected 10 more true positives than RT and 4 false positives were corrected from RT. This represents 14 inaccurate RT results that were corrected by DNA measurement. Therefore, DNA measurement should be fully considered as a screening method in the detection of HIV among MSM in the future.

Systematic review of the performance and clinical utility of point of care HIV-1 RNA testing for diagnosis and care

BACKGROUND

Point of-care (POC) HIV-1 RNA tests which are accurate and easy to use with limited infrastructure are needed in resource-limited settings (RLS). We systematically reviewed evidence of POC test performance compared to laboratory-based HIV-1 RNA assays and the potential utility of these tests for diagnosis and care in RLS.

METHODS

Studies published up to July 2018 were identified by a search of PUBMED, EMBASE, Web of Science, CINAHL and Cochrane Central Register of Controlled Trials. Studies evaluating the use of POC HIV-1 RNA testing for early infant diagnosis (EID), acute HIV infection (AHI) diagnosis, or viral load monitoring (VL), compared to centralized testing, were included. Separate search strategies were used for each testing objective.

RESULTS

197 abstracts were screened and 34 full-text articles were assessed, of which 32 met inclusion criteria. Thirty studies evaluated performance and diagnostic accuracy of POC tests compared to standard reference tests. Two of the thirty and two additional studies with no comparative testing reported on clinical utility of POC results. Five different POC tests (Cepheid GeneXpert HIV-1 Quantitative and Qualitative assays, Alere q HIV-1/2 Detect, SAMBA, Liat HIV Quant and Aptima HIV-1 Quant) were used in 21 studies of VL, 11 of EID and 2 of AHI. POC tests were easy to use, had rapid turnaround times, and comparable accuracy and precision to reference technologies. Sensitivity and specificity were high for EID and AHI but lower for VL. For VL, lower sensitivity was reported for whole blood and dried blood spots compared to plasma samples. Reported error rates for Cepheid GeneXpert Qual (2.0%-5.0%), GeneXpert Quant (2.5%-17.0%) and Alere q HIV-1/2 Detect (3.1%-11.0%) were higher than in WHO prequalification reports. Most errors resolved with retesting; however, inadequate sample volumes often precluded repeat testing. Only two studies used POC results for clinical management, one for EID and another for VL. POC EID resulted in shorter time-to-result, rapid ART initiation, and better retention in care compared to centralised testing.

CONCLUSIONS

Performance of POC HIV-1 RNA tests is comparable to reference assays, and have potential to improve patient outcomes. Additional studies on implementation in limited-resources settings are needed.

Point-of-care HIV testing best practice for early infant diagnosis: an implementation study

Background

With Universal Health Coverage and Integrated People-centred Health Care, streamlined health-systems and respectful care are necessary. South Africa has made great strides in prevention of mother-to-child transmission (PMTCT) but with the great burden of HIV, a minimum of birth and 10-week HIV-PCR testing are required for the estimated 360,000 HIV-exposed infants born annually which presents many challenges including delayed results and loss to follow-up. Point-of-care (POC) HIV testing of infants addresses these challenges well and facilitates initiation of HIV-infected infants rapidly after diagnosis for best clinical outcomes.

Methods

Objectives were to determine accuracy, feasibility and acceptability of POC testing compared to standard-of-care (SOC) central-laboratory testing. HIV-exposed infants for birth PCR testing in hospital (n = 323) and follow-up at a primary health care clinic (n = 117) in Durban, South Africa were included. A baseline situational-analysis reviewed registers and phoned mothers of HIV-exposed infants prior to the intervention. An effectiveness-implementation study of the Alere™q HIV-1/2 Detect POC test (heel-prick specimen processed in 50 min) was compared with SOC with questionnaires to mothers and staff. Stata 14 was used for analysis.

Results

At baseline 2% of birth HIV tests were missed; only 40% of mothers could be contacted; 17% did not receive birth test result; 19% did not have a 10-week test; 39% had not received the 10-week results. There were 5(1.5%) HIV-infected and 318(98.5%) HIV-negative infants detected in hospital with all clinic babies negative. All positive infants commenced ART before discharge. Ultimately POC and SOC had perfect concordance but for 10 SOC tests researchers actively tracked-down results or repeated tests. Turn around times for SOC tests were on average 8-days (IQR 6-10  days) and for POC testing was 0-days. The POC error-rate was 9,6% with all giving a result when repeated. The majority of mothers (92%) preferred POC testing with 7% having no preference. No staff preferred SOC testing with 79% preferring POC and 21% having no preference.

Conclusions

Point-of-care HIV testing for EID is accurate, feasible and acceptable, with benefits of early ART for all positive infants at birth facilities. We recommend that it be considered best practice for EID.

Trial registration

ISRCTN38911104 registered 9 January 2018 – retrospectively registered.

Electronic supplementary material

The online version of this article (10.1186/s12889-019-6990-z) contains supplementary material, which is available to authorized users.

Hepatitis B Virus Blood Screening: Need for Reappraisal of Blood Safety Measures?

Over the past decades, the risk of HBV transfusion–transmission has been steadily reduced through the recruitment of volunteer donors, the selection of donors based on risk-behavior evaluation, the development of increasingly more sensitive hepatitis B antigen (HBsAg) assays, the use of hepatitis B core antibody (anti-HBc) screening in some low-endemic countries, and the recent implementation of HBV nucleic acid testing (NAT). Despite this accumulation of blood safety measures, the desirable zero risk goal has yet to be achieved. The residual risk of HBV transfusion–transmission appears associated with the preseroconversion window period and occult HBV infection characterized by the absence of detectable HBsAg and extremely low levels of HBV DNA. Infected donations tested false-negative with serology and/or NAT still persist and derived blood components were shown to transmit the virus, although rarely. Questions regarding the apparent redundancy of some safety measures prompted debates on how to reduce the cost of HBV blood screening. In particular, accumulating data strongly suggests that HBsAg testing may add little, if any HBV risk reduction value when HBV NAT and anti-HBc screening also apply. Absence or minimal acceptable infectious risk needs to be assessed before considering discontinuing HBsAg. Nevertheless, HBsAg remains essential in high-endemic settings where anti-HBc testing cannot be implemented without compromising blood availability. HBV screening strategy should be decided according to local epidemiology, estimate of the infectious risk, and resources.