A Risk Analysis for Airborne Pathogens with Low Infectious Doses: Application to Respirator Selection Against Coccidioides immitis Spores

Abstract

Probability models incorporating a deterministic versus stochastic infectious dose are described for estimating infection risk due to airborne pathogens that infect at low doses. Such pathogens can be occupational hazards or candidate agents for bioterrorism. Inputs include parameters for the infectious dose model, distribution parameters for ambient pathogen concentrations, the breathing rate, the duration of an exposure period, the anticipated number of exposure periods, and, if a respirator device is used, distribution parameters for respirator penetration values. Application of the models is illustrated with a hypothetical scenario involving exposure to Coccidioides immitis, a fungus present in soil in areas of the southwestern United States Inhaling C. immitis spores causes a respiratory tract infection and is a recognized occupational hazard in jobs involving soil dust exposure in endemic areas An uncertainty analysis is applied to risk estimation in the context of selecting respiratory protection with a desired degree of efficacy.

Differences in Host Innate Responses among Coccidioides Isolates in a Murine Model of Pulmonary Coccidioidomycosis

“…As discussed above, we observed a differential cytokine response to Coccidioides isolates used in the study, and the early innate immune response did not seem overly robust. With regard to the infectious dose in humans, neither the average nor the minimum dosage is known (52). The dose administered to the mice in our study is biologically relevant, as a host could inhale 100,000 or more arthroconidia during an acute environmental exposure.…”

Issues Affecting Respirator Selection for Workers Exposed to Infectious Aerosols: Emphasis on Healthcare Settings

“…This method has been applied to respirator selections for protecting against inhalational exposures to Bacillus anthracis spores (as a possible bioterrorism agent [Nicas & Hubbard, 2003;Nicas, Neuhaus, & Spear, 2000]), Mycobacterium tuberculosis (Nicas, 1995(Nicas, , 1996, and Coccidioides immitis (Nicas & Hubbard, 2002).…”

“…The data used to compute the cumulative risk of an infectious aerosol are estimates of the infectious inhalational dose of an infectious agent, the air concentration of infectious particles, the respirator user's breathing rate, the fractional penetration value of the user's respirator, the duration of a respirator use period, and the number of respirator use periods (Nicas & Hubbard, 2002Nicas et al, 2000). Limitations of this method are that complete information is seldom available, and, as is true when applying the hazard ratio method to infectious aerosols, that important data-the infectious inhalational dose and the air concentrations of infectious particles to which workers may be exposed-are usually quite uncertain.…”

High resolution provenancing of long travelled dust deposited on the Southern Alps, New Zealand

“…The emerging significance of long travelled dust in global climate dynamics (Tegen et al, 1996;Kaufman et al, 2002;Claquin et al, 2003), regional air quality (Chan et al, 1999;Prospero, 1999), nutrient cycling and ocean fertilization (Gao et al, 2003;Boyd et al, 2004), and as a vector for the spread of pathogens (Nicas and Hubbard, 2002) has stimulated research efforts to better understand the transport history of long travelled aeolian dust. Historically, this has been achieved through analysis of surface meteorological observations and more recently satellite imagery from the Total Ozone Mapping Spectrometer (TOMS) (Herman et al, 1997;Prospero et al, 2002) and the Advanced Very High Resolution Radiometer (AVHRR) (Husar et al, 1997).…”