Background Immunoglobulin A (IgA) is an important component of the early immune response to SARS-CoV-2. Prior serosurveys in high-risk groups employing IgG testing alone have provided discordant estimates. The potential added benefit of IgA in serosurveys has not been established. Methods Longitudinal serosurvey of first responders (police, emergency medical service providers, fire fighters, and other staff) employing 3 serologic tests (anti-spike IgA, anti-spike IgG, and anti-nucleocapsid IgG) correlated with surveys assessing occupational and nonoccupational risk, exposure to COVID-19, and illnesses consistent with COVID-19. Results Twelve percent of first responders in Colorado at baseline and 22% at follow-up were assessed as having SARS-CoV-2 infection. Five percent at baseline and 6% at follow-up were seropositive only for IgA. Among those IgA positive only at baseline, the majority (69%) had a positive antibody at follow-up; 45% of those infected at baseline and 33% at follow-up were asymptomatic. At all time points, the estimated cumulative incidence in our study was higher than that in the general population. Conclusions First responders are at high risk of infection with SARS-CoV-2. IgA testing identified a significant portion of cases missed by IgG testing and its use as part of serologic surveys may improve retrospective identification of asymptomatic infection.

中文翻译：

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抗 SARS-CoV-2 IgA 可识别急救人员的无症状感染

背景 免疫球蛋白 A (IgA) 是对 SARS-CoV-2 的早期免疫反应的重要组成部分。之前对仅使用 IgG 检测的高危人群进行的血清调查提供了不一致的估计。IgA 在血清学调查中的潜在附加益处尚未确定。方法 使用 3 种血清学检测（抗尖峰 IgA、抗尖峰 IgG 和抗核衣壳 IgG）的急救人员（警察、紧急医疗服务提供者、消防员和其他工作人员）的纵向血清调查与评估职业和非职业风险的调查相关、暴露于 COVID-19 以及与 COVID-19 一致的疾病。结果 科罗拉多州 12% 的第一响应者在基线和 22% 的后续响应中被评估为感染了 SARS-CoV-2。基线时 5% 和随访时 6% 仅对 IgA 呈血清阳性。在仅在基线时 IgA 阳性的患者中，大多数（69%）在随访时抗体呈阳性；45% 的基线感染者和 33% 的后续感染者无症状。在所有时间点，我们研究中估计的累积发病率均高于一般人群。结论 急救人员感染 SARS-CoV-2 的风险很高。IgA 检测发现了 IgG 检测漏诊的很大一部分病例，将其用作血清学调查的一部分可能会改善对无症状感染的回顾性识别。结论 急救人员感染 SARS-CoV-2 的风险很高。IgA 检测发现了 IgG 检测漏诊的很大一部分病例，将其用作血清学调查的一部分可能会改善对无症状感染的回顾性识别。结论 急救人员感染 SARS-CoV-2 的风险很高。IgA 检测发现了 IgG 检测漏诊的很大一部分病例，将其用作血清学调查的一部分可能会改善对无症状感染的回顾性识别。