During the ongoing coronavirus disease (COVID-19) pandemic, farmworkers in the United States are considered essential personnel and continue in-person work. We conducted prospective surveillance for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and antibody prevalence among farmworkers in Salinas Valley, California, during June 15–November 30, 2020. We observed 22.1% (1,514/6,864) positivity for SARS-CoV-2 infection among farmworkers compared with 17.2% (1,255/7,305) among other adults from the same communities (risk ratio 1.29, 95% CI 1.20–1.37). In a nested study enrolling 1,115 farmworkers, prevalence of current infection was 27.7% among farmworkers reporting > 1 COVID-19 symptom and 7.2% among farmworkers without symptoms (adjusted odds ratio 4.16, 95% CI 2.85–6.06). Prevalence of SARS-CoV-2 antibodies increased from 10.5% (95% CI 6.0%–18.4%) during July 16–August 31 to 21.2% (95% CI 16.6%–27.4%) during November 1–30. High SARS-CoV-2 infection prevalence among farmworkers underscores the need for vaccination and other preventive interventions.

Key Points Question What are the risk factors associated with SARS-CoV-2 infection among farmworkers in California? Findings In this cross-sectional study of 1107 farmworkers, both household and workplace risk factors, including living with children aged 5 years or younger or unrelated roommates and living or working with an individual with known or suspected COVID-19, were associated with positive results on transcription-mediated amplification tests and immunoglobulin G tests for SARS-CoV-2 infection. Meaning These findings suggest that urgent distribution of vaccines to farmworkers and intervention on modifiable risk factors for SARS-CoV-2 infection are warranted given this population’s increased risk and the essential nature of their work.

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The only licensed dengue vaccine, Dengvaxia®, increases risk of severe dengue when given to individuals without prior dengue virus (DENV) infection but is protective against future disease in those with prior DENV immunity. The World Health Organization has recommended using rapid diagnostic tests (RDT) to determine history of prior DENV infection and suitability for vaccination. Dengue experts recommend that these assays be highly specific (≥98%) to avoid erroneously vaccinating individuals without prior DENV infection, as well as be sensitive enough (≥95%) to detect individuals with a single prior DENV infection. We evaluated one existing and two newly developed anti-flavivirus RDTs using samples collected >6 months post-infection from individuals in non-endemic and DENV and ZIKV endemic areas. We first evaluated the IgG component of the SD BIOLINE Dengue IgG/IgM RDT, which was developed to assist in confirming acute/recent DENV infections (n=93 samples). When evaluated following the manufacturer’s instructions, the SD BIOLINE Dengue RDT had 100% specificity for both non-endemic and endemic samples but low sensitivity for detecting DENV seropositivity (0% non-endemic, 41% endemic). Sensitivity increased (53% non-endemic, 98% endemic) when tests were allowed to run beyond manufacturer recommendations (0.5 up to 3 hours), but specificity decreased in endemic samples (36%). When tests were evaluated using a quantitative reader, optimal specificity could be achieved (≥98%) while still retaining sensitivity at earlier timepoints in non-endemic (44-88%) and endemic samples (31-55%). We next evaluated novel dengue and Zika RDTs developed by Excivion to detect prior DENV or ZIKV infections and reduce cross-flavivirus reactivity (n=207 samples). When evaluated visually, the Excivion Dengue RDT had sensitivity and specificity values of 79%, but when evaluated with a quantitative reader, optimal specificity could be achieved (≥98%) while still maintaining moderate sensitivity (48-75%). The Excivion Zika RDT had high specificity (>98%) and sensitivity (>93%) when evaluated quantitatively, suggesting it may be used alongside dengue RDTs to minimize misclassification due to cross-reactivity. Our findings demonstrate the potential of RDTs to be used for dengue pre-vaccination screening to reduce vaccine-induced priming for severe dengue and show how assay design adaptations as well quantitative evaluation can further improve RDTs for this purpose.

Estimation of community-level antibody responses to SARS-CoV-2 from infection or vaccination is critical to inform public health responses. Traditional studies of antibodies rely on collection of blood via venipuncture, an invasive procedure not amenable to pandemic-related social-distancing measures.

As essential personnel, United States farmworkers have continued working in-person throughout the COVID-19 pandemic. We undertook prospective surveillance of SARS-CoV-2 infection and antibody prevalence among farmworkers in California’s Salinas Valley from 15 June to 30 November, 2020. Over this period, we observed 22.1% (1514/6864) positivity for current SARS-CoV-2 by nucleic acid detection among farmworkers tested at federally-qualified migrant and community health clinics, as compared to 17.2% (1255/7305) among other adults from the same communities (risk ratio, 1.29; 95% confidence interval, 1.20-1.37). In a nested study enrolling 1,115 farmworkers, prevalence of current infection was 27.7% among farmworkers reporting ≥1 potential COVID-19 symptom, and 7.2% among farmworkers without symptoms (adjusted odds ratio 4.17; 2.86-6.09). Prevalence of anti-SARS-CoV-2 IgG antibodies increased from 10.5% (6.0-18.4%) between 16 July-31 August to 21.2% (16.6-27.4%) between 1-30 November. The high observed prevalence of infection among farmworkers underscores the need for vaccination and other preventive interventions.

pH tuning of hydrogen-bonding interactions between polymers within layer-by-layer films controls temperature-triggered pyrene release.

Importance: Essential workers in agriculture and food production have been severely affected by the ongoing COVID-19 pandemic. Objective: To identify risk factors associated with SARS-CoV-2 shedding and antibody response in farmworkers in California. Design: This cross-sectional study collected survey data and determined current SARS-CoV-2 shedding and seropositivity among 1,107 farmworkers in California's Salinas Valley from 16 July to 30 November 2020. Setting: Farmworkers receiving transcription-mediated amplification (TMA) tests for SARS-CoV-2 infection at federally qualified community clinics and community sites were invited to participate in our study. Participants: Individuals were eligible if they were not pregnant, were 18 years old or older, had conducted farm work since the pandemic started, and were proficient in English or Spanish. Exposures: Sociodemographic, household, community, and workplace characteristics. Main Outcome(s) and Measure(s): Current (as indicated by TMA positivity) and historical (as indicated by IgG seropositivity) SARS-CoV-2 infection. Results: Most farmworkers enrolled in the study were born in Mexico, had primary school or lower levels of educational attainment, and were overweight or obese. Current SARS-CoV-2 shedding was associated in multivariable analyses with attained only primary or lower educational levels (RR=1.32; 95% CI: 0.99-1.76), speaking an indigenous language at home (RR=1.30; 0.97-1.73), working in the fields (RR=1.60; 1.03-2.50), and exposure to known or suspected COVID-19 case at home (RR=2.98; 2.06-4.32) or in the workplace (RR=1.59; 1.18-2.14). Antibody detection was associated with residential exposures including living in crowded housing (RR=1.23; 0.98-1.53), with children (RR=1.40; 1.1-1.76) or unrelated roommates (RR=1.40; 1.19-1.64), and with a known or suspected COVID-19 case (RR=1.59; 1.13-2.24). Those who were obese (RR=1.65; 1.01-2.70) or diabetic (RR=1.31; 0.98-1.75) were also more likely to be seropositive. Farmworkers who lived in rural areas other than Greenfield (RR=0.58; 0.47-0.71), worked indoors (RR=0.68; 0.61-0.77), or whose employer provided them with information on how to protect themselves at work (RR=0.59; 0.40-0.86) had lower risk of prior infection.