Measuring Haitian children's exposure to chikungunya, dengue and malaria

Chikungunya Outbreak Risks after the 2014 Outbreak, Dominican Republic

The 2014 chikungunya outbreak in the Dominican Republic resulted in intense local transmission, with high postoutbreak seroprevalence. The resulting population immunity will likely minimize risk for another large outbreak through 2035, but changes in population behavior or environmental conditions or emergence of different virus strains could lead to increased transmission.

Adaptation to a Multiplex Bead Assay and Seroprevalence to Rift Valley Fever N Protein: Nampula Province, Mozambique, 2013-2014

Rift Valley fever virus (RVFV) is endemic in sub-Saharan Africa (SSA), with outbreaks reported in the Arabian Peninsula and throughout SSA. The natural reservoir for RVFV are ruminants, with livestock populations exceeding 50% exposure rates in some areas of SSA. Transmission to humans can occur through exposure to infected livestock products or multiple species of mosquito vectors. In 2013 and 2014, cross-sectional surveys occurred in two districts of Nacala-a-Velha and Mecubúri in northern Mozambique, and participants provided blood samples for later serological assays. IgG against the N protein of RVFV was detected through multiplex bead assay (MBA). Of the 2,278 persons enrolled between the two surveys and study sites, 181 (7.9%, 95% confidence interval (CI): 6.9%-9.1%) were found to be IgG seropositive with increasing seroprevalence with older age and significantly higher seroprevalence in Nacala-a-Velha (10.5%, 8.8%-12.5%) versus Mecubúri (5.7%, 4.5%-7.1%). Seroprevalence estimates were not significantly different between the 2013 and 2014 surveys. Significant spatial clustering of IgG positive persons were consistent among surveys and within the two districts, pointing toward the consistency of serology data for making population-level assumptions regarding RVFV seroprevalence. A subset of persons (n = 539) provided samples for both the 2013 and 2014 surveys, and a low percentage (0.81%) of these were found to seroconvert between these two surveys. Including the RVFV N protein in an MBA antigen panel could assist elucidate RVFV exposure in SSA. IMPORTANCE Due to sporadic transmission, human contact with Rift Valley Fever Virus (RVFV) is difficult to ascertain at a population level. Detection of antibodies against RVFV antigens assist in estimating exposure as antibodies remain in the host long after the virus has been cleared. In this study, we show that antibodies against RVFV N protein can be detected from dried blood spot (DBS) samples being assayed by multiplex bead assay. DBS from two districts in northern Mozambique were tested for IgG against the N protein, and 7.9% of all enrolled persons were seropositive. Older persons, males, and persons residing closer to the coast had higher RVFV N protein seroprevalence. Spatial clustering of IgG positive persons was noted in both districts. These results show low exposure rates to RVFV in these two northern districts in Mozambique, and the ability to perform serology for the RVFV N protein from dried blood samples.

Multiplex Serology for Measurement of IgG Antibodies Against Eleven Infectious Diseases in a National Serosurvey: Haiti 2014-2015

Background

Integrated surveillance for multiple diseases can be an efficient use of resources and advantageous for national public health programs. Detection of IgG antibodies typically indicates previous exposure to a pathogen but can potentially also serve to assess active infection status. Serological multiplex bead assays have recently been developed to simultaneously evaluate exposure to multiple antigenic targets. Haiti is an island nation in the Caribbean region with multiple endemic infectious diseases, many of which have a paucity of data for population-level prevalence or exposure.

Methods

A nationwide serosurvey occurred in Haiti from December 2014 to February 2015. Filter paper blood samples (n = 4,438) were collected from participants in 117 locations and assayed for IgG antibodies on a multiplex bead assay containing 15 different antigens from 11 pathogens: Plasmodium falciparum, Toxoplasma gondii, lymphatic filariasis roundworms, Strongyloides stercoralis, chikungunya virus, dengue virus, Chlamydia trachomatis, Treponema pallidum, enterotoxigenic Escherichia coli, Entamoeba histolytica, and Cryptosporidium parvum.

Results

Different proportions of the Haiti study population were IgG seropositive to the different targets, with antigens from T. gondii, C. parvum, dengue virus, chikungunya virus, and C. trachomatis showing the highest rates of seroprevalence. Antibody responses to T. pallidum and lymphatic filariasis were the lowest, with <5% of all samples IgG seropositive to antigens from these pathogens. Clear trends of increasing seropositivity and IgG levels with age were seen for all antigens except those from chikungunya virus and E. histolytica. Parametric models were able to estimate the rate of seroconversion and IgG acquisition per year for residents of Haiti.

Conclusions

Multiplex serological assays can provide a wealth of information about population exposure to different infectious diseases. This current Haitian study included IgG targets for arboviral, parasitic, and bacterial infectious diseases representing multiple different modes of host transmission. Some of these infectious diseases had a paucity or complete absence of published serological studies in Haiti. Clear trends of disease burden with respect to age and location in Haiti can be used by national programs and partners for follow-up studies, resource allocation, and intervention planning.

Antenatal Seroprevalence of Zika and Chikungunya Viruses, Kingston Metropolitan Area, Jamaica, 2017–2019

To determine the extent of exposure to Zika virus (ZIKV) and chikungunya virus (CHIKV) in Jamaica, we collected serum from 584 pregnant women during 2017–2019. We found that 15.6% had antibodies against ZIKV and 83.6% against CHIKV. These results indicate potential recirculation of ZIKV but not CHIKV in the near future.

Integrated serological surveillance of acute febrile illness in the context of a lymphatic filariasis survey in Timor-Leste: a pilot study using dried blood spots

Background

Acute febrile illnesses (AFIs), including dengue, scrub typhus and leptospirosis, cause significant morbidity and mortality in Southeast Asia. Serological surveillance can be used to investigate the force and distribution of infections. Dried blood spot (DBS) samples are an attractive alternative to serum because they are easier to collect and transport and require less cold storage. We conducted a pilot study to determine the feasibility of integrating serological surveillance for dengue, scrub typhus and leptospirosis into a population-representative lymphatic filariasis seroprevalence survey in Timor-Leste using DBSs.

Methods

A total of 272 DBSs were collected from healthy community participants. DBSs were analysed at the National Health Laboratory using commercially available enzyme-linked immunosorbent assays. To validate assays for DBSs, 20 anonymised serum samples of unknown serostatus were used to create dried serum spots (DSSs). These were analysed with optical densities compared with those of serum. Where low variance was observed (dengue assay) the published kit cut-offs for serum were applied to the analysis of DBSs. For the other assays (scrub typhus and leptospirosis), index values (IVs) were calculated and cut-offs were determined to be at 2 standard deviations (SDs) above the mean.

Results

Of the 272 samples analysed, 19 (7.0% [95% confidence interval {CI} 4.3 to 10.7]) were positive for dengue immunoglobulin G (IgG), 11 (4.0% [95% CI 2.1 to 7.1]) were positive for scrub typhus IgG and 16 (5.9% [95% CI 3.4 to 9.4%]) were positive for leptospira IgG.

Conclusions

While dengue seroprevalence was lower than in nearby countries, results represent the first evidence of scrub typhus and leptospirosis transmission in Timor-Leste. Integrated programmes of serological surveillance could greatly improve our understanding of infectious disease epidemiology in remote areas and would incur minimal additional fieldwork costs. However, when planning such studies, the choice of assays, their validation for DBSs and the laboratory infrastructure and technical expertise at the proposed location of analysis must be considered.

Determining seropositivity-A review of approaches to define population seroprevalence when using multiplex bead assays to assess burden of tropical diseases

Background

Serological surveys with multiplex bead assays can be used to assess seroprevalence to multiple pathogens simultaneously. However, multiple methods have been used to generate cut-off values for seropositivity and these may lead to inconsistent interpretation of results. A literature review was conducted to describe the methods used to determine cut-off values for data generated by multiplex bead assays.

Methodology/Principal findings

A search was conducted in PubMed that included articles published from January 2010 to January 2020, and 308 relevant articles were identified that included the terms “serology”, “cut-offs”, and “multiplex bead assays”. After application of exclusion of articles not relevant to neglected tropical diseases (NTD), vaccine preventable diseases (VPD), or malaria, 55 articles were examined based on their relevance to NTD or VPD. The most frequently applied approaches to determine seropositivity included the use of presumed unexposed populations, mixture models, receiver operating curves (ROC), and international standards. Other methods included the use of quantiles, pre-exposed endemic cohorts, and visual inflection points.

Conclusions/Significance

For disease control programmes, seropositivity is a practical and easily interpretable health metric but determining appropriate cut-offs for positivity can be challenging. Considerations for optimal cut-off approaches should include factors such as methods recommended by previous research, transmission dynamics, and the immunological backgrounds of the population. In the absence of international standards for estimating seropositivity in a population, the use of consistent methods that align with individual disease epidemiological data will improve comparability between settings and enable the assessment of changes over time.

Serological surveys can provide information regarding population-level disease exposure by assessing immune responses created during infection. Multiplex bead assays (MBAs) allow for an integrated serological platform to monitor antibody responses to multiple pathogens concurrently. As programs adopt integrated disease control strategies, MBAs are especially advantageous since many of these diseases may be present in the same population and antibodies against all pathogens of interest can be detected simultaneously from a single blood sample. Interpreting serological data in a programmatic context typically involves classifying individuals as seronegative or seropositive using a ‘cut-off’, whereby anyone with a response above the defined threshold is considered to be seropositive. Although studies increasingly test blood samples with MBAs, published studies have applied different methods of determining seropositivity cut-offs, making results difficult to compare across settings and over time. The lack of harmonized methods for defining seropositivity is due to the absence of international standards, pathogen biology, or assay-specific methods that may impact resulting data. This review highlights the need for a standardized approach for which cut-off methods to use per pathogen when applied to integrated disease surveillance using platforms such as MBAs.

Anti-chikungunya virus seroprevalence in Indigenous groups in the São Francisco Valley, Brazil

Background

Chikungunya fever (CHIKF) is a serious public health problem with a high rate of infection and chronic disabling manifestations that has affected more than 2 million people worldwide since 2005. In spite of this, epidemiological data on vulnerable groups such as Indigenous people are scarce, making it difficult to implement public policies in order to prevent this disease and assist these populations.

Objective

To describe the serological and epidemiological profile of chikungunya virus (CHIKV) in two Indigenous populations in Northeast Brazil, as well as in an urbanized control community, and to explore associations between CHIKV and anthropometric variables in these populations.

Methodology/Principal findings

This is a cross-sectional ancillary study of the Project of Atherosclerosis among Indigenous Populations (PAI) that included people 30 to 70 years old, recruited from two Indigenous tribes (the less urbanized Fulni-ô and the more urbanized Truká people) and an urbanized non-Indigenous control group from the same area. Subjects underwent clinical evaluation and were tested for anti-CHIKV IgG by enzyme-linked immunosorbent assay. Serological profile was described according to ethnicity, sex, and age. The study population included 433 individuals distributed as follows: 109 (25·2%) Truká, 272 (62·8%) Fulni-ô, and 52 (12%) from the non-Indigenous urbanized control group. Overall prevalence of CHIKV IgG in the study sample was 49.9% (216; 95% CI: 45·1–54·7). When the sample was stratified, positive CHIKV IgG was distributed as follows: no individuals in the Truká group, 78·3% (213/272; 95% CI: 72·9–83·1) in the Fulni-ô group, and 5.8% (3/52; 95% CI: 1.21–16) in the control group.

Conclusions/Significance

Positive tests for CHIKV showed a very high prevalence in a traditional Indigenous population, in contrast to the absence of anti-CHIKV serology in the Truká people, who are more urbanized with respect to physical landscape, socio-cultural, and historical aspects, as well as a low prevalence in the non-Indigenous control group, although all groups are located in the same area.

Chikungunya fever is a serious public health problem, with a high rate of infection and disease. Chikungunya virus (CHIKV) is a cosmopolitan virus, which has inflicted severe damage in 50 countries in the Americas and is responsible for chronic disabling manifestations. In spite of this, epidemiological data on vulnerable groups such as Indigenous people are scarce. We report on a cross-sectional study describing the seroprevalence of CHIKV in Indigenous groups in the São Francisco Valley, Brazil, in association with anthropometric data. The study population included 433 individuals distributed in the following ethnic groups: 109 (25.2%) Truká, 272 (62·8%) Fulni-ô, and 52 (12%) from the non-Indigenous urbanized control group When the sample was stratified, positive CHIKV IgG was distributed as follows: no individuals in the Truká group, 213/272 (78.3%; 95% CI: 72·9–83·1) individuals in the Fulni-ô group, and 3/52 (5.8%; 95% CI: 1·21–16) individuals in the control group. This study shows, for the first time, that CHIKV circulated in an Indigenous population (Fulni-ô) in the São Francisco Valley, in 2016 and 2017. The finding strikingly differs from the absence of anti-CHIKV serology found in the Truká people and from the low prevalence in the urban region of Juazeiro, Bahia.

Optimisation and standardisation of a multiplex immunoassay of diverse Plasmodium falciparum antigens to assess changes in malaria transmission using sero-epidemiology

Background: Antibody responses have been used to characterise transmission and exposure history in malaria-endemic settings for over a decade. Such studies have typically been conducted on well-standardised enzyme-linked immunosorbent assays (ELISAs). However, recently developed quantitative suspension array technologies (qSAT) are now capable of high-throughput and multiplexed screening of up to hundreds of analytes at a time. This study presents a customised protocol for the Luminex MAGPIX © qSAT using a diverse set of malaria antigens. The aim is to develop a standardised assay for routine serological surveillance that is implementable across laboratories and epidemiological settings. Methods: A panel of eight Plasmodium falciparum recombinant antigens, associated with long- and short-lived antibody responses, was designed for the Luminex MAGPIX © platform. The assay was optimised for key steps in the protocol: antigen-bead coupling concentration, buffer composition, serum sample dilution, and bead storage conditions. Quality control procedures and data normalisation methods were developed to address high-throughput assay processing.  Antigen-specific limits of quantification (LOQs) were also estimated using both in-house and WHO reference serum as positive controls. Results: Antigen-specific bead coupling was optimised across five serum dilutions and two positive controls, resulting in concentrations operational within stable analytical ranges. Coupled beads were stable after storage at room temperature (22⁰C) for up to eight weeks. High sensitivity and specificity for distinguishing positive and negative controls at serum sample dilutions of 1:500 (AUC 0.94 95%CI 0.91-0.96) and 1:1000 (AUC 0.96 95%CI 0.94-0.98) were observed. LOQs were also successfully estimated for all analytes but varied by antigen and positive control. Conclusions: This study demonstrates that developing a standardised malaria-specific qSAT protocol for a diverse set of antigens is achievable, though further optimisations may be required. Quality control and data standardisation methods may also be useful for future analysis of large sero-epidemiological surveys.

Optimisation and standardisation of a multiplex immunoassay of diverse Plasmodium falciparum antigens to assess changes in malaria transmission using sero-epidemiology

Background: Antibody responses have been used to characterise transmission and exposure history in malaria-endemic settings for over a decade. Such studies have typically been conducted on well-standardised enzyme-linked immunosorbent assays (ELISAs). However, recently developed quantitative suspension array technologies (qSAT) are now capable of high-throughput and multiplexed screening of up to hundreds of analytes at a time. This study presents a customised protocol for the Luminex MAGPIX ^© qSAT using a diverse set of malaria antigens. The aim is to develop a standardised assay for routine serological surveillance that is implementable across laboratories and epidemiological settings.

Methods: A panel of eight Plasmodium falciparum recombinant antigens, associated with long- and short-lived antibody responses, was designed for the Luminex MAGPIX ^© platform. The assay was optimised for key steps in the protocol: antigen-bead coupling concentration, buffer composition, serum sample dilution, and bead storage conditions. Quality control procedures and data normalisation methods were developed to address high-throughput assay processing.  Antigen-specific limits of quantification (LOQs) were also estimated using both in-house and WHO reference serum as positive controls.

Results: Antigen-specific bead coupling was optimised across five serum dilutions and two positive controls, resulting in concentrations operational within stable analytical ranges. Coupled beads were stable after storage at room temperature (22⁰C) for up to eight weeks. High sensitivity and specificity for distinguishing positive and negative controls at serum sample dilutions of 1:500 (AUC 0.94 95%CI 0.91-0.96) and 1:1000 (AUC 0.96 95%CI 0.94-0.98) were observed. LOQs were also successfully estimated for all analytes but varied by antigen and positive control.

Conclusions: This study demonstrates that developing a standardised malaria-specific qSAT protocol for a diverse set of antigens is achievable, though further optimisations may be required. Quality control and data standardisation methods may also be useful for future analysis of large sero-epidemiological surveys.

Measuring Cryptosporidium Serologic Responses by Multiplex Bead Assay

For more than 35 years, various assay formats have been used to detect Cryptosporidium-specific antibodies in human and animal sera. Cryptosporidium parvum 17- and 27-kDa antigens, identified from invasive sporozoites, have been used in serologic antibody assays to identify individuals infected in outbreaks of diarrheal disease caused by this protozoan parasite and to monitor exposures in communities. During infection, immunoglobulin (Ig) A, IgM, and IgG responses are elicited by these immunodominant antigens, and the parasite-specific Ig responses diminish following the resolution of infection. Using the recombinant forms of the 17- and 27-kDa C. parvum antigens and the relatively recently developed multiplex bead assay (MBA), data from serologic antibody responses can be economically and efficiently acquired, especially when the Cryptosporidium assays are integrated with assays for antibody responses to antigens from other pathogens monitored in community-wide or nation-wide serosurveys. Here we describe the coupling of the C. parvum recombinant antigens to carboxylated polystyrene beads, the data acquisition and analysis of IgG antibodies bound to the coupled beads, and the quality control methods required for data validation using the Luminex/MBA system.

Serological Data Shows Low Levels of Chikungunya Exposure in Senegalese Nomadic Pastoralists

The chikungunya virus (CHIKV) is spread by Aedes aegypti and Ae. albopictus mosquitos worldwide; infection can lead to disease including joint pain, fever, and rash, with some convalescent persons experiencing chronic symptoms. Historically, CHIKV transmission has occurred in Africa and Asia, but recent outbreaks have taken place in Europe, Indonesia, and the Americas. From September to October 2014, a survey was undertaken with nomadic pastoralists residing in the northeast departments of Senegal. Blood dried on filter paper (dried blood spots; DBS) were collected from 1465 participants of all ages, and assayed for Immunoglobulin G (IgG) antibodies against CHIKV E1 antigen by a bead-based multiplex assay. The overall seroprevalence of all participants to CHIKV E1 was 2.7%, with no persons under 10 years of age found to be antibody positive. Above 10 years of age, clear increases of seroprevalence and IgG levels were observed with increasing age; 7.6% of participants older than 50 years were found to be positive for anti-CHIKV IgG. Reported net ownership, net usage, and gender were all non-significant explanatory variables of seropositivity. These data show a low-level historical exposure of this pastoralist population to CHIKV, with no evidence of recent CHIKV transmission in the past decade.

Integrated Serologic Surveillance of Population Immunity and Disease Transmission

Antibodies are unique among biomarkers in their ability to identify persons with protective immunity to vaccine-preventable diseases and to measure past exposure to diverse pathogens. Most infectious disease surveillance maintains a single-disease focus, but broader testing of existing serologic surveys with multiplex antibody assays would create new opportunities for integrated surveillance. In this perspective, we highlight multiple areas for potential synergy where integrated surveillance could add more value to public health efforts than the current trend of independent disease monitoring through vertical programs. We describe innovations in laboratory and data science that should accelerate integration and identify remaining challenges with respect to specimen collection, testing, and analysis. Throughout, we illustrate how information generated through integrated surveillance platforms can create new opportunities to more quickly and precisely identify global health program gaps that range from undervaccination to emerging pathogens to multilayered health disparities that span diverse communicable diseases.

Use of Bead-Based Serologic Assay to Evaluate Chikungunya Virus Epidemic, Haiti

The index case of chikungunya virus (CHIKV) in Haiti was reported during early 2014; the vector, the pervasive Aedes aegypti mosquito, promoted rapid spread throughout the country. During December 2014–February 2015, we collected blood samples from 4,438 persons at 154 sites (62 urban, 92 rural) throughout Haiti and measured CHIKV IgG by using a multiplex bead assay. Overall CHIKV seroprevalence was 57.9%; differences between rural (mean 44.9%) and urban (mean 78.4%) areas were pronounced. Logistic modeling identified the urban environment as a strong predictor of CHIKV exposure (adjusted odds ratio 3.34, 95% CI 2.38–4.69), and geographic elevation provided a strong negative correlation. We observed no correlation between age and antibody positivity or titer. Our findings demonstrated through serologic testing the recent and rapid dissemination of the arbovirus throughout the country. These results show the utility of serologic data to conduct epidemiologic studies of quickly spreading mosquitoborne arboviruses.

The impact of school water, sanitation, and hygiene improvements on infectious disease using serum antibody detection

Background

Evidence from recent studies assessing the impact of school water, sanitation and hygiene (WASH) interventions on child health has been mixed. Self-reports of disease are subject to bias, and few WASH impact evaluations employ objective health measures to assess reductions in disease and exposure to pathogens. We utilized antibody responses from dried blood spots (DBS) to measure the impact of a school WASH intervention on infectious disease among pupils in Mali.

Methodology/Principal findings

We randomly selected 21 beneficiary primary schools and their 21 matched comparison schools participating in a matched-control trial of a comprehensive school-based WASH intervention in Mali. DBS were collected from 20 randomly selected pupils in each school (n = 807). We analyzed eluted IgG from the DBS using a Luminex multiplex bead assay to 28 antigens from 17 different pathogens. Factor analysis identified three distinct latent variables representing vector-transmitted disease (driven primarily by dengue), food/water-transmitted enteric disease (driven primarily by Escherichia coli and Vibrio cholerae), and person-to-person transmitted enteric disease (driven primarily by norovirus). Data were analyzed using a linear latent variable model. Antibody evidence of food/water-transmitted enteric disease (change in latent variable mean (β) = -0.24; 95% CI: -0.53, -0.13) and person-to-person transmitted enteric disease (β = -0.17; 95% CI: -0.42, -0.04) was lower among pupils attending beneficiary schools. There was no difference in antibody evidence of vector-transmitted disease (β = 0.11; 95% CI: -0.05, 0.33).

Conclusions/Significance

Evidence of enteric disease was lower among pupils attending schools benefitting from school WASH improvements than students attending comparison schools. These findings support results from the parent study, which also found reduced incidence of self-reported diarrhea among pupils of beneficiary schools. DBS collection was feasible in this resource-poor field setting and provided objective evidence of disease at a low cost per antigen analyzed, making it an effective measurement tool for the WASH field.

Trial registration

The trial was registered at ClinicalTrials.gov (NCT01787058)

Water, sanitation, and hygiene (WASH) in schools is promoted as an intervention to improve child health in low-resource settings. However, evidence of the impact of school WASH interventions on child health is mixed. One reason could be that most studies rely on self-reported disease symptoms, which are prone to bias. In order to objectively measure evidence of disease, we collected dried blood spots (DBS) from pupils attending schools participating in an impact evaluation of a comprehensive school WASH intervention in Mali, and analyzed the DBS for antibody responses to 28 antigens from 17 different pathogens. We found that evidence of enteric disease was lower among pupils attending beneficiary schools compared to pupils attending comparison schools. These results are consistent with those from the parent study, which also found reduced self-reported diarrhea among pupils attending beneficiary schools. Our results support WASH in schools as an effective intervention to improve child health. Further, DBS are a feasible measurement tool for the WASH field to provide objective evidence of disease.

Measuring changes in transmission of neglected tropical diseases, malaria, and enteric pathogens from quantitative antibody levels

BACKGROUND

Serological antibody levels are a sensitive marker of pathogen exposure, and advances in multiplex assays have created enormous potential for large-scale, integrated infectious disease surveillance. Most methods to analyze antibody measurements reduce quantitative antibody levels to seropositive and seronegative groups, but this can be difficult for many pathogens and may provide lower resolution information than quantitative levels. Analysis methods have predominantly maintained a single disease focus, yet integrated surveillance platforms would benefit from methodologies that work across diverse pathogens included in multiplex assays.

METHODS/PRINCIPAL FINDINGS

We developed an approach to measure changes in transmission from quantitative antibody levels that can be applied to diverse pathogens of global importance. We compared age-dependent immunoglobulin G curves in repeated cross-sectional surveys between populations with differences in transmission for multiple pathogens, including: lymphatic filariasis (Wuchereria bancrofti) measured before and after mass drug administration on Mauke, Cook Islands, malaria (Plasmodium falciparum) before and after a combined insecticide and mass drug administration intervention in the Garki project, Nigeria, and enteric protozoans (Cryptosporidium parvum, Giardia intestinalis, Entamoeba histolytica), bacteria (enterotoxigenic Escherichia coli, Salmonella spp.), and viruses (norovirus groups I and II) in children living in Haiti and the USA. Age-dependent antibody curves fit with ensemble machine learning followed a characteristic shape across pathogens that aligned with predictions from basic mechanisms of humoral immunity. Differences in pathogen transmission led to shifts in fitted antibody curves that were remarkably consistent across pathogens, assays, and populations. Mean antibody levels correlated strongly with traditional measures of transmission intensity, such as the entomological inoculation rate for P. falciparum (Spearman's rho = 0.75). In both high- and low transmission settings, mean antibody curves revealed changes in population mean antibody levels that were masked by seroprevalence measures because changes took place above or below the seropositivity cutoff.

CONCLUSIONS/SIGNIFICANCE

Age-dependent antibody curves and summary means provided a robust and sensitive measure of changes in transmission, with greatest sensitivity among young children. The method generalizes to pathogens that can be measured in high-throughput, multiplex serological assays, and scales to surveillance activities that require high spatiotemporal resolution. Our results suggest quantitative antibody levels will be particularly useful to measure differences in exposure for pathogens that elicit a transient antibody response or for monitoring populations with very high- or very low transmission, when seroprevalence is less informative. The approach represents a new opportunity to conduct integrated serological surveillance for neglected tropical diseases, malaria, and other infectious diseases with well-defined antigen targets.