Department of Environmental Health, Harvard T. H. Chan School of Public Health, Boston, USA.
BMC Infect Dis. 2020 Jul 11;20(1):497. doi: 10.1186/s12879-020-05200-6.
The spread of airborne infectious diseases such as measles is a critical public health concern. The U.S. was certified measles-free in 2000, but the number of measles cases has increased in recent years breaking the record of the nationwide annual number of cases since 1992. Although the characteristics of schools have made them one of the most vulnerable environments during infection outbreaks, the transmission risk of measles among students is not completely understood. We aimed to evaluate how three factors influence measles transmission in schools: personal (vaccination), social (compartmentalizing), and building systems (ventilation, purification, and filtration).
We used a combination of a newly developed multi-zone transient Wells-Riley approach, a nationwide representative School Building Archetype (SBA) model, and a Monte-Carlo simulation to estimate measles risk among U.S. students. We compared our risk results with the range of reported transmission rates of measles in school outbreaks to validate the risk model. We also investigated the effectiveness of vaccination and ten supplemental infection control scenarios for reducing the risk of measles transmission among students.
Our best nationwide estimate of measles transmission risk in U.S. schools were 3.5 and 32% among all (both unvaccinated and immunized) and unvaccinated students, respectively. The results showed the transmission risk of measles among unvaccinated students is > 70 times higher than properly immunized ones. We also demonstrated that the transmission risk of measles in primary schools (assuming teacher self-contained classrooms) is less than secondary schools (assuming departmentalized systems). For building-level interventions, schools with ductless-with-air-filter and ductless-without-air-filter systems have the lowest and highest transmission risks of measles, respectively. Finally, our simulation showed that infection control strategies could cut the average number of infected cases among all students in half when a combination of advanced air filtration, ventilation, and purification was adopted in the modeled schools.
Our results highlight the primary importance of vaccination for reducing the risk of measles transmission among students. Yet, additional and significant risk reduction can be achieved through compartmentalizing students and enhancing building ventilation and filtration systems.
麻疹等空气传播传染病的传播是一个重大的公共卫生问题。美国在 2000 年已被认证为无麻疹国家，但近年来麻疹病例数量有所增加，打破了自 1992 年以来全国年度病例数的纪录。尽管学校的特点使其成为感染爆发期间最脆弱的环境之一，但麻疹在学生中的传播风险尚不完全清楚。我们旨在评估个人（疫苗接种）、社会（隔离）和建筑系统（通风、净化和过滤）三个因素如何影响学校的麻疹传播。
我们结合了一种新开发的多区域瞬态 Wells-Riley 方法、一个全国代表性的学校建筑原型 (SBA) 模型和蒙特卡罗模拟，以估计美国学生中的麻疹风险。我们将风险结果与麻疹在学校爆发中的报告传播率范围进行比较，以验证风险模型。我们还研究了疫苗接种和十种补充感染控制方案在降低学生麻疹传播风险方面的有效性。
我们对美国学校麻疹传播风险的最佳全国估计是，所有（未接种和已接种）和未接种学生的麻疹传播风险分别为 3.5%和 32%。结果表明，未接种学生的麻疹传播风险比正确接种的学生高 70 多倍。我们还表明，小学（假设教师自我隔离教室）的麻疹传播风险低于中学（假设部门化系统）。对于建筑层面的干预措施，带空气过滤器的无管道系统和无空气过滤器的无管道系统的麻疹传播风险最低和最高。最后，我们的模拟表明，当在模型学校中采用先进的空气过滤、通风和净化的组合时，感染控制策略可以将所有学生中感染病例的平均数量减少一半。
我们的结果强调了疫苗接种对于降低学生麻疹传播风险的首要重要性。然而，通过隔离学生和增强建筑通风和过滤系统，可以进一步显著降低风险。
