Abstract

Legionella pneumophila is an opportunistic bacterial respiratory pathogen that is one of the leading causes of drinking water outbreaks in the United States. Dental offices pose a potential risk for inhalation or aspiration of L. pneumophila due to the high surface area to volume ratio of dental unit water lines—a feature that is conducive to biofilm growth. This is coupled with the use of high-pressure water devices (e.g., ultrasonic scalers) that produce fine aerosols within the breathing zone. Prior research confirms that L. pneumophila occurs in dental unit water lines, but the associated human health risks have not been assessed. We aimed to: (1) synthesize the evidence for transmission and management of Legionnaires’ disease in dental offices; (2) create a quantitative modeling framework for predicting associated L. pneumophila infection risk; and (3) highlight influential parameters and research gaps requiring further study. We reviewed outbreaks, management guidance, and exposure studies and used these data to parameterize a quantitative microbial risk assessment (QMRA) model for L. pneumophila in dental applications. Probabilities of infection for dental hygienists and patients were assessed on a per-exposure and annual basis. We also assessed the impact of varying ventilation rates and the use of personal protective equipment (PPE). Following an instrument purge (i.e., flush) and with a ventilation rate of 1.2 air changes per hour, the median per-exposure probability of infection for dental hygienists and patients exceeded a 1-in-10,000 infection risk benchmark. Per-exposure risks for workers during a purge and annual risks for workers wearing N95 masks did not exceed the benchmark. Increasing air change rates in the treatment room from 1.2 to 10 would achieve an ∼85% risk reduction, while utilization of N95 respirators would reduce risks by ∼95%. The concentration of L. pneumophila in dental unit water lines was a dominant parameter in the model and driver of risk. Future risk assessment efforts and refinement of microbiological control protocols would benefit from expanded occurrence datasets for L. pneumophila in dental applications.

摘要

Legionella pneumophila是一种机会性细菌呼吸道病原体，是美国饮用水爆发的主要原因之一。由于牙科治疗台水线的高表面积与体积比，牙科诊所存在吸入或误吸嗜肺军团菌的潜在风险——这一特征有利于生物膜的生长。这与在呼吸区内产生细小气溶胶的高压水设备（例如，超声波洁牙机）的使用相结合。先前的研究证实，嗜肺军团菌发生在牙科治疗台水管中，但尚未评估相关的人类健康风险。我们的目标是：（1）综合有关牙科诊所军团病传播和管理的证据；(2) 创建用于预测相关嗜肺军团菌感染风险的定量建模框架；(3) 突出有影响的参数和需要进一步研究的研究空白。我们审查了暴发、管理指南和暴露研究，并使用这些数据来参数化嗜肺军团菌的定量微生物风险评估 (QMRA) 模型在牙科应用中。牙科保健员和患者的感染概率在每次接触和每年的基础上进行评估。我们还评估了不同通风率和使用个人防护设备 (PPE) 的影响。在器械清洗（即冲洗）和每小时换气 1.2 次的情况下，牙科保健员和患者的每次暴露感染概率中值超过了 10,000 分之一的感染风险基准。清洗期间工人的单次暴露风险和戴 N95 口罩的工人的年度风险未超过基准。将治疗室的换气率从 1.2 增加到 10 可将风险降低约 85%，而使用 N95 呼吸器可将风险降低约 95%。嗜肺军团菌的浓度在牙科治疗台中，水线是模型中的主要参数和风险驱动因素。未来的风险评估工作和微生物控制协议的改进将受益于牙科应用中嗜肺军团菌的扩展发生数据集。