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

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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