W o r k h t p t l p a : / c / e w a w n The Spread of Airborne Infectious Disease w d . I e n a t d . l o t o h r . s A e / e Christopher Chao, PhD r a o e r s Department of Mechanicaol Enginoeering l s s o The Hong Kong University of Scienlce and 2 s 0 Technology, China 2 1 0 2 1 2 Motivation of the Work Airborne transmission disease W o r k h t p t l p a : / c / e w a w n w d . I Measles [Department of Health, HKSAR Govt,] e M. Tuberculosis [International Union Against n a t d Tuberculosis and Lung Disease] . l o t o Infamous outbreak cases in various envirohnments r . s A e / e r a o e r s o o l s s o l 2 s 0 2 1 0 2 1 2 AMOY garden was the most seriously A TB outbreak case in an economy cabin on a flight affected location during the 2003 SARS from Chicago to Honolulu in April 1994. (Kenyon et al. outbreak, with over 300 infected people. 1996) (Li et al. 2004) Guidelines on Airborne Transmission Disease Control W o r k h t p t l p a : / c / e ASHRAE’s w WHO NATURAL a w n recommendation VENTILATION GUIDELINE w d . I e • A strategic research agenda has been n a developed to address the role of HVAC systemts d• For natural ventilation, the following minimum . in the spread of infectious disease; l ohourly averaged ventilation rates should be t porovided: • The topic is included in ASHRAE’s future h r strategic plans; .• 160 l/ s/patient (hourly average ventilation rate) sfor airborne precaution rooms (with a minimum of • Further research should be conducted to A e8/0 l/s/pateient) (note that this only applies to new understand how reducing the energy footprint heaalth-care fracilities and major renovations); of buildings will impact infectious disease o • 60 l/es/patient for general wards and outpatient transmission; r s departments; and • Further research should be conducted on o o • 2.5 l/s/m3 for corridorls and other transient spaces engineering controls to reduce infectious s s without a fixed number of patients; however, disease transmission. The document o l summarizes the control strategies available and when patient care is undert2aken in corridors s the occupancy categories in which these during emergency or other sit0uations, the same 2 ventilation rate requirements fo1r airborne controls can be used. The research priority for 0 precaution rooms or general wards2 will apply. each control is provided. Filtration and UVGI 1 controls research are given top priority because 2 less is known about how these controls can be applied in buildings and HVAC systems to decrease disease events. ASHRAE. 2009. ASHRAE Position Document on Airborne Infectious Diseases. WHO. 2009. Natural Ventilation for Infection Control in Health-Care Settings. Formulation of the Problem W o r - Expiratory droplets and droplet k h t p nuclei can be airborne carriers for t l various pathogens (e.g. M. p a : / c Tuberculosis, measles, influenza, / e etc). w a w n w d . I- Epidemiology studies showed that e n a these infectious diseases can be t d . transmitted indoors following the l o t veontilation air. h r . [Department of Medical Microbiology, s A e Edinburgh University] / e r a o e r s o o l s Inhalation s Pathogen-laden o l Aerosols 2 s 0 2 1 0 2 1 2 Infectious Source Solid Surface (Fomite) Susceptible Epidemiologic Approach W o The epidemiology profession has developed a number of widely accepted steps r k to investigahte disease outbreaks. t p t l p a : / c / e w Disease Veraify the diagnosis Identify the w n outbreak wrelatded to the existence of the . I eoutbreak outbreak n a t d . l o t Prevent o h r . s Create a casAe definition to define e Develop and / e who/what is incrluded as a case a implement control e o r s and prevention o o l s systems s o l Map the spread of the outbre2ak s 0 2 1 0 2 1 2 Study & refine hypothesis Develop a hypothesis WStudy of airborne infectious disease o r k h t p t l p a : • Size distr/ibutcion of the exhaled droplets / e w a • How the drwopletsn disperse? w d . I e n • What are their faates? Deposited? Exhausted? t d . l o t o • Any chance to re-sushp.end rf rom the surfaces? s A e / e r • What is the infection riska? o e r s o o l • Any method to reduce the infsection risk? s o l 2 s 0 2 1 0 2 1 2 Studies on Expiratory Aerosol Size Distribution W o r k h t p • Expiratotry dropllets evaporate to nuclei and the diameter may reduce p a : to around ha/lf of thce initial size. The smaller nuclei can be / e suspended in awir. a w n • Collecting media awnd microdscopic measurement were applied to . I e reveal the size distribution of enxpiratory aerosols by numerous a t d . studies, such as Duguid, 194l6 and oLouden and Roberts, 1967. t o h r • The geometric mean diameter o.f particl es from coughing were 12 s A e μm from Duguid and 14 μm from L/oudon eand Roberts. (Nicas et al. r a 2005) e o r s o o l s s o l 2 s 0 2 1 0 Duguid J.P. 1946. The size and duration of air-carriage of respiratory droplets and droplet-nuclei. J. Hyg, 4, 471–480. 2 1 Loudon R.G, and Roberts R.M. 1967. Droplet expulsion from the respiratory tract. Am. Rev. Resp. Dis., 95, 435–442. 2 Nicas M, Nazaroff W.W, and Hubbard A. 2005. Toward understanding the risk of secondary airborne infection: emission of respiratory pathogens. Journal of Occupational and Environmental Hygiene, 2:3, 143-154. Studies on Expiratory Aerosol Size Distribution W o Measured by SMPS and particle counter, tidal r k h breathting flpow rate varied from 0.27 to 0.70l/s, t l p a exhaled v:olume ranged from 0.35 to 1.70l. / c / e w a w n The range of Cough flow rate was from 1.6-8.5l/s, w d . I Cough expired volueme vanried from 0.25-1.60l. a t d . l o t o h r PIV measurement on cough. veloc ity for 29 volunteers: s A e Maximum velocity of cough at/ diffeerent distances r a o from mouth ranged from 1.5 to e28.8m/s, with r s o o average of 10.2m/s. l s s o l 2 s 0 2 PIV Average cough velocity was 11.2 m/s. 1 0 2 1 2 Holmgren H, Ljungstrom E, Almstrand A.C, Bake B, and Olin A.C. 2010. Journal of Aerosol Science, 41, 439-446. Gupta J.K, Lin C.H, and Chen Q. 2009. Indoor Air, 19:517-525. VanSciver M, Miller S, and Hertzberg J. 2011. Aerosol Science and Technology, 45:415-422. Zhu S, Kato S, and Yang J.H. 2006. Building and Environment, 41, 1691–1702. Studies on Expiratory Aerosol Size Distribution W o Methods Size (μm) r k Heymann eht al. 1899 Solid impaction (glass slide with microscope) 30-500 t p t l Strauz et al. 192p6 a Solid impaction (glass slide with microscope) 70-85 : / c Jennision, 1942 / High-speed photography >100 e w Duguid et al. 1946 Soalid impaction (glass slide with microscope) 100-125 w n Gerone et al. 1966 Solid impaction, Liquid impaction <1.0-1.0 w d . I Loudon et al. 1967 eSolid impaction (paper with microscope) 55.5 n a Papineni et al. 1997 t Optdical particle counter <0.6 . l o t Fennelly et al. 2004 Solid impaction (omulti-stages impactor) ≦3.3 h r . Yang et al. 2007 APS, SMPS 0.62-15.9 s A e Xie et al. 2009 Solid impaction (glass slid/e with miecroscope), Dust monitor 50-75 r a Wainwright et al. 2009 Solid impaction (muelti-stages oimpactor) ≦3.3 r s Li et al. 2008 Solid impaction (glass slide with moicroscopeo), Dust monitor 50-100 l s Morawska et al. 2008 APS s 0.1-1.0 o l 2 Chao et al. 2009 IMI s 4-8 0 2 1 Morawska et al. 2009 APS 0 0.4-10.0 2 1 Li et al. 2010 APS, IMI, microscope 2 >50 Johnson et al. 2011 APS, droplet deposition analysis 0.7->20 Gralton J, Tovey E, McLaws M.L, and Rawlinson W.D. 2011. The role of particle size in aerosolised pathogen transmission: a review. Journal of Infection, 62, 1-13. StuWdies on Expiratory Aerosol Size Distribution o r k h t p t l p a : • Cough je/t velcocity / e w a • Size distribuwtion n w d . I e n – Interferometric aMie Imaging, APS, Droplet t d . l o t Deposition Analysis o h r . s A – Evaporation of droplets e / e r a o e – Respiratory activities r s o o l s s – Origins o l 2 s 0 2 1 0 2 1 2