Aerosol Generation, Ventilation and Risk Assessment

Transcription

1 Aerosol Generation, Ventilation and Risk Assessment CDC Biosafety Symposium 2014

2 Contents Laboratory Acquired Infection and Aerosols ( ). Where the regulations came from How many Pascals? The Laboratory Protection Factor An introduction to Microbial Aerosols Aerosol Generation in the Modern Microbiology Laboratory Gloves and laboratory discipline 2 BEDA Business plan

3 Laboratory Acquired Infections ( ) - Aerosols & Outbreaks A Sharples centrifuge used for centrifuging live Brucella organisms leading to 45 clinical cases and one death was located in the hallway of the basement. 20 lab workers infected with VEE when 9 freeze dried ampoules dropped Numerous Q fever outbreaks associated with buildings centrifuging and blending infected eggs 3 died of glanders following centrifuge accident 11 cases of typhus due to intranasal infection of mice Many of these associated with biological weapons research. High titre, high aerosol risk.

4 Laboratory Acquired Infections (Pike 1976) CAUSE AGENT Accident 17.9 Animal or ectoparasite 16.8 Clinical Specimen 7.3 Glassware 1.2 Autopsy 1.9 Intentional Infection 0.5 Aerosols (known) 13.3 Work with agent 21.1 Others, unknown 20.0 Brucellosis 426 (5) Q fever 280 (1) Hepatitis 268 (3) Typhoid fever 256(20) Tularemia 225 (2) Tuberculosis 194 (4) Typhus 124 Psittacosis 116 (10) Leptospirosis 78 Streptococci 87

5 Smallpox Lab 1978

6 Aerosols, Aerosols, Aerosols The focus on lab safety was now firmly on prevention of aerosol transmission as: The report concluded an aerosol route of infection The distance this aerosol had to travel The lab contained a malfunctioning cabinet The tragic outcome Control measures can be monitored Therefore as regulations were developed it was focussed on preventing a recurrence Decency prevented focussing on the human factors behind the outbreak Overwork Poor training Lack of separation between safety and management Rumours of a relationship between the professor and the victim

7 Negative Pressure How many Pascals? 7

8 Introduction How many Pascals? Do I need an anteroom? 8

9 How Many Pascals Do I Need? In a UK survey a range of Pa was encountered Imploding laboratories UK Guidance (ACDP) -40Pa, -70Pa for Cat 4 Calibration Testing of aerosol release during entry and exit from laboratories was undertaken using the Potassium Iodide method 9

10 When a Laboratory Is At Negative Pressure To The Rest of The Building And The Doors Are Closed No Microbial Aerosol Will Be Released Into The Building Aerosol Release Will Only Occur When The Lab Doors Are Opened

11 Laboratory Protection Factor (LPF) LPF = Laboratory aerosol Released aerosol

12 LPF v DP for Lab Entry Laboratory Protection Factor 10 5 Anteroom LPF was less than 4.4 x Maximimum Pressure Differential (Pa) LPF for lab without anteroom 1.5 x 10 3

13 LPF v Inflow for Lab Entry Laboratory Protection Factor 10 5 Operational Laboratory Experimental Laboratory Volumetric Inflow (m 3 sec -1 )

14 LPF v Inflow for Anteroom Entry Laboratory Protection Factor Anteroom, Cat 3 Lab Corridor, Cat 3 Labs Anteroom, Experimental Room Corridor, Experimental Room Laboratory Inflow (m 3 min -1 )

15 Conclusions of Study Laboratory Protection Factor is a useful measure of containment LPF is proportional to inflow velocity and not pressure differentials Anterooms increase containment fold An inflow of 10m 3 /min through a standard laboratory door (0.17m 3 /sec) gives LPF of ca

16 Aerosol Generation The modern BSL3 laboratory is designed to control workers being exposed to aerosols and aerosols leaving the facility. This governs requirements for Filtration Negative pressure Safety cabinets While we can measure the protection afforded by these measures to ensure they are adequate we need to know something about aerosols generated within the microbiology laboratory 16

17 Introduction to Aerobiology Deposition & Exposure Deposition Velocity (u) = d p2 g 18 The deposition velocity is directly proportional to the particle diameter squared Particle size also influences deposition in the respiratory tract Deposition Velocity (cm/sec) Aerodynamic Particle Diameter (microns) V=4/3πr 3 The cube rule. The number of micro-organisms in a 10 micron particle will be 1000 times those in a 1 micron particle 10 micron particle has volume 1.3x 10-9 mls

18 Where do aerosols come from? Bennett & Parks (2006) Accident (10 9 spore/ml suspension) Aerosol Generated (cfu/l of air) Centrifuge Rotor 23.0 Leak * Flask Break in 1.15 Shaking Incubator * Dropping Large 2l 13.7 Bottle * 15ml Spill from 1m * 2.07 A direct relationship was found between titre and aerosol concentration. The lower the titre the less likely is that significant aerosol exposure will occur 50% of aerosol particles were less than 3 microns 18

19 Where do aerosols come from and how do we prevent them Bennett & Parks (2006) Accident (10 9 spore/ml suspension) Aerosol Generated (cfu/l of air) CONTROL Centrifuge Rotor Leak * 23.0 SEALED ROTOR Flask Break in Shaking 1.15 USE Incubator * PLASTICWARE Dropping Large 2l 13.7 USE Bottle * PLASTICWARE 15ml Spill from 1m * 2.07 WORK IN CABINET 19

20 Aerosol Generation from Pipetting Aerosol Generation from Serial Diluting a Spore Solution Total Average CFU Average Time Taken (Seconds) Experienced Inexperienced Average Time Taken Participant 0 20

21 Visual Contamination for Serial Diluting Procedure Participant Surface Gloves Experienced 1 N.D. N.D. 2 2 N.D. 3 N.D. N.D. 4 N.D. N.D. 5 N.D. N.D. 6 N.D. N.D. 7 N.D. N.D. Inexperienced 1 >10 N.D. 2 N.D. N.D. 3 N.D. N.D. 4 N.D. N.D. 5 1 N.D. 21

22 Aerosols from Plating Out Aerosol Generation from Plating Out and Spreading a Spore Solution Total Average CFU Average Time Taken (Seconds) Experienced Inexperienced Average Time Taken Participant 0 22

23 Visual Contamination for Plating Out Procedure Participant Surface Gloves Experienced 1 9 N.D. 2 >10 N.D. 3 > N.D. 5 7 N.D. 6 7 N.D Inexperienced 1 >10 N.D. 2 8 N.D. 3 2 N.D >10 N.D. 23

24 60 Aerosol Generation from Serial Diluting a Spore Solution Containment Level 3 Trained Non Containment Level 3 Trained 50 Total Average CFU Participant Experienced Inexperienced 24

25 Conclusions In most cases aerosols should not be generated in a laboratory Any aerosols should be contained in primary containment To create a significant aerosol you need a high titre agents Unrecognised surface contamination occurs Training can reduce the extent of aerosol and surface contamination 25 BEDA Business plan

26 Gloves and Laboratory Acquired Infection 26

27 Causes of Laboratory Acquired Infections Davies review to be published Cause Number % Needlestick/accidental inoculation Open Bench working (no clear exposure) Aerosol exposure suspected 8 12 Contact/Ingestion/mouth pipetting Unknown/no information given 7 10 Improper Inactivation

28 Clinical cases of hep B/ persons and year ((health care staff, upper line, and general population years, lower line Gloves Prevent Direct Contact health care staff vaccination Infection Six episodes of MRSA contamination were detected from 20 hand-washing episodes where the technician did not use latex gloves, as compared to one MRSApositive culture from 51 handwashing episodes where he or she used latex gloves (risk ratio 15.3, P < 0.05). No potential pathogens were cultured from any hand episodes following hand washing. Ng et al 2011 Bacterial contamination of hands and the environment in a microbiology laboratory 28 Journal of Hospital Infection Volume 78, Issue

29 Laboratory Discipline & Biosafety Compliance Someone is watching you (BSL2) 29 Compliance with Glove Use Only 46% of staff removed gloves on leaving BSL2 lab Hand hygiene compliance before exiting laboratory was 10.3% (0-85%) in labs. Training was not predictive Face Touching 72% touched face during study 3.4 contacts per hour Wide variation between labs Nose> Forehead> Cheek> Mouth>Eye Face touching linked to vaccinia and meningitidis lab infections James Johnston, University of Utah, ABSA conference 2010.

30 Outbreak of Salmonella Typhimurium Infections Associated with Exposure to Clinical & Teaching Microbiology Laboratories CDC April 28 th 2011 Illnesses identified among students in teaching laboratories and employees in clinical microbiology laboratories. Ill persons (60%) were significantly more likely than control persons (2%) to report exposure to a microbiology laboratory in the week before the illness began. multiple ill persons reported working specifically with Salmonella bacteria in microbiology laboratories. The outbreak strain was indistinguishable from a commercially available Salmonella Typhimurium strain used in several laboratories associated with people infected with the outbreak strain. Several children who live in households with a person who works or studies in a microbiology laboratory have become ill with the outbreak strain. 30

31 CONCLUSIONS Aerosols are not the only source of infection. Designing facilities to prevent aerosol transmission is very expensive Since the regulations were written aerosol control methods have become widely available We still have problems in the developed world with compliance to simple cost effective protective measures We need to educate, train and ensure compliance in good microbiological and biosafety practise Aerosols can also be avoided by good practise 31

32 32 Questions?