A novel method for determining whole house particle removal and clean air delivery rates attributable to central and portable ventilation/air cleaning systems is described. The method is used to characterize total and air-cleaner-specific particle removal rates during operation of four in-duct air cleaners and two portable air-cleaning devices in a fully instrumented test home. Operation of in-duct and portable air cleaners typically increased particle removal rates over the baseline rates determined in the absence of operating a central fan or an indoor air cleaner. Removal rates of 0.3- to 0.5-microm particles ranged from 1.5 hr(-1) during operation of an in-duct, 5-in. pleated media filter to 7.2 hr(-1) for an in-duct electrostatic air cleaner in comparison to a baseline rate of 0 hr(-1) when the air handler was operating without a filter. Removal rates for total particulate matter less than 2.5 microm in aerodynamic diameter (PM2.5) mass concentrations were 0.5 hr(-1) under baseline conditions, 0.5 hr(-1) during operation of three portable ionic air cleaners, 1 hr(-1) for an in-duct 1-in. media filter, 2.4 hr(-1) for a single high-efficiency particle arrestance (HEPA) portable air cleaner, 4.6 hr(-1) for an in-duct 5-in. media filter, 4.7 hr(-1) during operation of five portable HEPA filters, 6.1 hr(-1) for a conventional in-duct electronic air cleaner, and 7.5 hr(-1) for a high efficiency in-duct electrostatic air cleaner. Corresponding whole house clean air delivery rates for PM2.5 attributable to the air cleaner independent of losses within the central ventilation system ranged from 2 m3/min for the conventional media filter to 32 m3/min for the high efficiency in-duct electrostatic device. Except for the portable ionic air cleaner, the devices considered here increased particle removal indoors over baseline deposition rates.

Health risks of fine particle air pollution (PM 2.5 ) are an important public health concern that has the potential to be mitigated in part by interventions such as air cleaning devices that reduce personal exposure to ambient PM 2.5 . To characterize exposure to ambient PM 2.5 indoors as a function of residential air cleaners, a multi-zone indoor air quality model was used to integrate spatially resolved data on housing, meteorology, and ambient PM 2.5 , with performance testing of residential air cleaners to estimate short-term and annual average PM 2.5 of outdoor origin inside residences of three metropolitan areas. The associated public health impacts of reduced ambient PM 2.5 exposure were estimated using a standard health impact assessment methodology. Estimated indoor levels of ambient PM 2.5 varied substantially among ventilation and air cleaning configurations. The median 24-h average indooroutdoor ratio of ambient PM 2.5 was 0.57 for homes with natural ventilation, 0.35 for homes with central air conditioning (AC) with conventional filtration, and 0.1 for homes with central AC with high efficiency in-duct air cleaner. Median modeled 24-h average indoor concentrations of PM 2.5 of outdoor origin for those three configurations were 8.4, 5.3, and 1.5 mg/m 3 , respectively. The potential public health benefits of reduced exposure to ambient PM 2.5 afforded by air cleaning systems were substantial. If the entire population of single-family homes with central AC in the modeling domain converted from conventional filtration to high-efficiency in-duct air cleaning, the change in ambient PM 2.5 exposure is estimated to result in an annual reduction of 700 premature deaths, 940 hospital and emergency room visits, and 130,000 asthma attacks in these metropolitan areas. In addition to controlling emissions from sources, high-efficiency whole-house air cleaner are expected to reduce exposure to particles of outdoor origin and are projected to be an effective means of managing public health impacts of ambient particle pollution.

Human behaviour will continue to play an important role as the world grapples with public health threats. In this paper, we draw from the emerging evidence on behaviour adoption during diverse public health emergencies to develop a framework that contextualises behaviour adoption vis-à-vis a combination of top-down, intermediary and bottom-up approaches. Using the COVID-19 pandemic as a case study, we operationalise the contextual framework to demonstrate how these three approaches differ in terms of their implementation, underlying drivers of action, enforcement, reach and uptake. We illustrate how blended strategies that include all three approaches can help accelerate and sustain protective behaviours that will remain important even when safe and effective vaccines become more widely available. As the world grapples with the COVID-19 pandemic and prepares to respond to (re)emerging public health threats, our contextual framework can inform the design, implementation, tracking and evaluation of comprehensive public health and social measures during health emergencies.

Background In 2010, Mexico was the most common (22.9%) country of origin for foreign-born persons with tuberculosis in the United States, and overall trends in tuberculosis morbidity are substantially influenced by the Mexico-born population. Objectives To determine the risk of tuberculosis disease among Mexico-born persons living in the United States. Methods Using data from the U.S. National Tuberculosis Surveillance System and the American Community Survey, we examined tuberculosis case counts and case rates stratified by years since entry into the United States and geographic proximity to the United States–Mexico border. We calculated trends in case rates over time measured by average annual percent change. Results The total tuberculosis case count (−14.5%) and annual tuberculosis case rate (average annual percent change −5.1%) declined among Mexico-born persons. Among those diagnosed with tuberculosis less than 1 year since entry into the United States (newly arrived persons), there was a decrease in tuberculosis cases (−60.4%), no change in tuberculosis case rate (average annual percent change of 0.0%), and a decrease in population (−60.7%). Among those living in the United States for more than 5 years (non-recently arrived persons), there was an increase in tuberculosis cases (+3.4%), a decrease in tuberculosis case rate (average annual percent change of −4.9%), and an increase in population (+62.7%). In 2010, 66.7% of Mexico-born cases were among non–recently arrived persons, compared with 51.1% in 2000. Although border states reported the highest proportions (>15%) of tuberculosis cases that were Mexico-born, the highest Mexico-born–specific tuberculosis case rates (>20/100,000 population) were in states in the eastern and southeastern regions of the United States. Conclusions The decline in tuberculosis morbidity among Mexico-born persons may be attributed to fewer newly arrived persons from Mexico and lower tuberculosis case rates among non–recently arrived Mexico-born persons. The extent of the decline was dampened by an unchanged tuberculosis case rate among newly arrived persons from Mexico and a large increase in the non–recently arrived Mexico-born population. If current trends continue, tuberculosis morbidity among Mexico-born persons will be increasingly driven by those who have been living in the United States for more than 5 years.