Natural Natural VentilationVentilation of Health Care of Health Care FacilitiesFacilities

HOSPITAL NACIONAL

“DOS DE MAYO”

Dr Rod Escombe MD DTM&H PhDHonorary Research Fellow, Wellcome Centre for Clinical Tropical Medicine & Department of Infectious Diseases & Immunity, Imperial College London, UK.Senior Investigator, Asociación Benéfica PRISMA, Lima, Perú. GP Registrar, St Mary’s Hospital, London, UK.

Engineering Methods for the Control of Airborne Infections: An International Perspective

Harvard School of Public Health20th July 2008

1.Bonifacio N. Emerg Inf Dis 2002;8:747 2.Joshi R. PLoS Med 2006; 3:494 3.Drobniewski F. PLoS Med 2007; 4:55

MDR, XDRHIV-TB

• Dilutional ventilation is the mainstay of environmental control measures for airborne infections

• Aim to reduce the concentration of infectious airborne particles

• Reduce exposure of patients, staff and visitors

Ventilation and control of airborne Ventilation and control of airborne infection in health care facilitiesinfection in health care facilities

0

20

40

60

80

100

0 1 2 3 4

Time (hours)

Con

cent

ratio

n (c

fu/m

3 )

1 ACH2

48

Measuring ventilation: Measuring ventilation: Air Changes per Hour (ACH)Air Changes per Hour (ACH)

Effect of ACH on concentration of airborne particles

Freshair

=

33:67%

Wells-Riley equation:

C=S(1-e –Iqpt/Q)

C= new cases S=susceptiblesI =number of infectors q=infectious quanta produced per hourp=pulmonary minute ventilationt=duration of exposureQ=absolute ventilation (= ACH x room volume)

Modelling Modelling effect of ventilation on effect of ventilation on airborne infectionairborne infection

Effect of dilutional ventilation on risk of Effect of dilutional ventilation on risk of airborne infectionairborne infection

Ventilation rate (h-1)

0 10 20 30Quanta

generation (quanta/m

in)

0

10

20

Risk

0

0.5

1

Yuguo Li

MechanicalMechanical ventilationventilation

• Air changes diluteinfectious particles

• Negative pressure

• Standard of care

CDC Guidelines 2005: 6-12 ACH for high-risk areas

Natural ventilationNatural ventilation

• Passive supply of outdoor air to a building interior for ventilation and cooling

• Historically all buildings employed natural ventilation

Pantheon, Rome – 120 AD

Natural ventilation in health care facilities

“The very first canon of nursing, the first and the last thing upon which a nurse’s attention must be fixed, the first essential to the patient, without which all the rest you can do for him is as nothing, with which I had almost said you may leave all the rest alone, is this: to keep the air he breathes as pure as the external air, without chilling him”

Notes on Nursing – What it is and what it is not. 1860. London

TB sanatoriaTB sanatoria• Pre-antibiotic era• Fresh air therapy

Midhurst, Sussex, UK

With modern building design, advent of HVAC, natural ventilation fell from favour

Renewed interest in Renewed interest in natural ventilationnatural ventilation

General building design• Need to reduce energy costs: “green buildings”

Health care facilities• TB & HIV epidemics, emergence of drug

resistance and recognition of nosocomial spread1

• TB prevention low resource settings. WHO 19992

• TB Infection control in era of HIV. WHO 20073

• Infection prevention and control of epidemic- and pandemic-prone acute respiratory diseases in health care. WHO Interim guidelines 20074

Evidence base so far is slim

• Data from Peru

1. Gandhi, N.R., et al. XDR-TB in South Africa. Lancet, 2006. 368:1575-80. 2. http://www.who.int/docstore/gtb/publications/healthcare/PDF/WHO99-269.pdf3. http://whqlibdoc.who.int/hq/1999/WHO_TB_99.269_ADD_eng.pdf4. http://www.who.int/csr/resources/publications/WHO_CD_EPR_2007_6/en/

World Health Organization

Natural ventilationNatural ventilation

• Simply opening windows• Low cost• Maintenance free• Climate dependant

Natural ventilation Natural ventilation –– basic principlesbasic principles

Cross ventilation Stack effect

Hot air rises

Natural ventilationNatural ventilation –– basic principlesbasic principles

Poor Improved

Layout

WHO guidelines

Martin Yag

Paul Jensen

Natural ventilation in Lima hospitalsNatural ventilation in Lima hospitals• 8 hospitals

– 5 old-fashioned design built pre-1950– 3 modern hospitals built 1970-90

• 70 naturally ventilated rooms

– Respiratory isolation rooms– TB, respiratory, infectious disease, HIV, general medical wards– Emergency departments– Out-patient clinics and waiting rooms

• 12 mechanically ventilated respiratory isolation rooms

– Built in 2000, renovated by Wellcome Trust in 2004