tb infection control: engineering (environmental) controls kevin p. fennelly, md, mph division of...
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TB Infection Control:Engineering (Environmental)
Controls
Kevin P. Fennelly, MD, MPHDivision of Pulmonary & Critical Care Medicine
Center for Emerging PathogensUMDNJ-New Jersey Medical School
Objectives• To review fundamental principles and practices of
TB infection control related to engineering controls
• To discuss advantages and limitations to different engineering control measures.
• To discuss how engineering controls are used in the total TB Infection Control Plan.
• To discuss issues and questions specific to your experiences in Chiapas.
Key Points• Engineering controls (EC) are the 2nd priority in
control measures AFTER administrative controls, • But they are complementary
• Dilution ventilation is the most important EC– Protects HCWs, other patients, visitors– Has limits defined by technology, expense, comfort
• Negative pressure or directional airfllow keeps contaminated air away from HCWs
• UVGI and filtration devices are adjuncts or back-ups for high-risk areas– Require maintenance– Need to consider cost-effectiveness
• Administrative controls: reduce risk of exposure
• Environmental controls: prevent spread and reduce concentration of droplet nuclei
• Respiratory protection controls: further reduce risk of exposure to wearer only
Fundamentals of Infection Control
Hierarchy of Infection Control
Respiratory Protection
Administrative Controls
Environmental Controls
Hierarchy of Infection Controls
Administrative
Administrative
Environmental
EnvironmentalRespiratory
Respiratory
protection
protection
Worke
r
Worke
r
Patient
Patient
Setting
Setting
TB-Infection Controls: Simplified
• Administrative: WHO?– Who is a TB suspect?– Who is at risk from exposure?– Who has infectious TB?– Who has drug resistant TB?
• Environmental: WHERE?– Where is optimal place to minimize risk?
• Personal Respiratory Protection: Special high risk settings
Environmental Controls
• Control source of infection
• Dilute and remove contaminated air
• Control airflow – Keep infectious air moving outside– Keep HCWs ‘upwind’ , infectious patients
‘downwind’
Airborne Infection Isolation Room Policies
• Environmental factors and entry of visitors and HCWs should be controlled
• Air changes per hour (ACH) (volume /time)– >6 ACH (existing)– >12 ACH (new)
• Minimum of 2 ACH of outdoor air• HCWs should wear at least N95 respirators
10
What is ventilation?
• Movement of air
• “Pushing” and/or “pulling” of particles and vapors
• Preferably in a controlled manner
11
Ventilation control• Types of ventilation
– Natural
– Local
– General
Local exhaust ventilation
• Source capture
– Exterior hoods
– Enclosing hoods
Uganda
Examples of General Ventilation
•Single pass– First choice
• Recirculating– HEPA filtration
14
Room Air Mixing and Air Flow
• Prevent air stagnation• Prevent short
circuiting• Air direction• Air temperature• Space configuration• Movement
• Clean to less clean
• Negative pressure
Facility Airflow Direction
• Clean to less clean
• Negative pressure
Facility Airflow Direction
17
BronchoscopyBronchoscopy
Brazil
18
- Escombe AR et al. Plos Med 2007 ; 4: e68
- Escombe AR et al. Plos Med 2007 ; 4: e68
Natural vs Mechanical Ventilation
• Good natural ventilation is better than bad mechanical ventilation.
• Major limitation of natural ventilation is that it depends upon outdoor weather conditions.
• Can control odor and improve comfort of occupants , but not if very cold or very hot.
• Usually we do not have a choice and must work with where we are!
Limitations of Ventilation
24
HEPA filtration
Must be used– When discharging air from local exhaust
ventilation booths or enclosures directly into the surrounding room, and
– When discharging air from an AII room into the general ventilation system
25
Room Air Cleaners
26TB Outpatient unit – Helio Fraga Institute, MoH, Rio de JaneiroTB Outpatient unit – Helio Fraga Institute, MoH, Rio de Janeiro
27
11
1010
100100
1,0001,000
00 22 44 66 88 1010
Elapsed Time (hours)Elapsed Time (hours)
Colo
ny F
orm
ing
Uni
ts (C
FUs)
Colo
ny F
orm
ing
Uni
ts (C
FUs)
Position 1 Position 2 Position 3Position 4Position 5Position 6Position 7Position 8Position 9
Linear
OffOff OnOn
Evaluation of Room Air Cleaners
28
Ultraviolet Germicidal Irradition (UVGI)
• Used as supplement or back-up to dilution ventilation
• Does NOT provide negative pressure
• Requires maintenance, esp. cleaning bulbs
• Not effective at high humidity (>70%)
• Occupational exposure limits: eye & skin
29
Xu P et al. Atmospheric Environment 2003; 37:405
31
- Escombe AR et al. Plos Med 2009 (March) ; 6
Escombe AR et al. Plos Med 2009 (March) ; 6
Environmental Controls: Which one and When?
• Dilution ventilation, UVGI, and HEPA filter units are all effective under IDEAL laboratory conditions
• Best data in field support dilution ventilation• Advantage of ventilation is usually ‘always on’,
minimizing human errors.• Disadvantages of UVGI and HEPAs
– Maintenance (increased human errors)– Large variability of effectiveness– May cause false sense of reassurance
Assumptions: Homogenous distribution of infectious aerosol over 10 hours; uniform susceptibility.
- Fennelly KP & Nardell EA. Infect Control Hosp Epidemiol 1998; 19;754
Control Measures are Synergistic & Complementary
Wells-Riley Equation: Mathematical model of airborne
infectionPr{infection}=C/S=1-e(-Iqpt/Q)
Where
C=# S infected x S=# susceptibles exposed xI = # infectors (# active pulm TB cases) xq = # infectious units produced/hr/Infector xp = pulm ventilation rate/hr/St = hours of exposure xQ = room ventilation rate with fresh air
x
Admin E.C.
Risk of Close Exposure?
HCWInfectious Case
Summary – TBIC Engineering Controls
• First priority is ADMINISTRATIVE controls, but EC are complementary
• Dilution ventilation is most important for all– Can add to comfort– But limited by technology, comfort, expense
• Negative pressure or directional airflow can keep infected air away (even if diluted) from HCWs
• UVGI and filtration devices are adjuncts for high risk areas– Back-up when not possible to ventilate well
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