DISINFECTION MISCONCEPTIONS

1
DISINFECTIONMISCONCEPTIONS

• Glenn A, Funk, Ph.D, CBSP

2
Why Disinfect?

• to get rid of unwanted pathogenic
  microorganisms
• To eliminate exposure risk
• medical waste treatment
• spill cleanup
• minimization of nosocomial infections
• routine surface decontamination
• To eliminate contamination risk
• preparation of microbiological media supplies
• preparation of pharmaceutical production supplies
  and equipment
• preparation of food (surface sanitization)
• prepn of work area for cleanliness-critical tasks

3
Resistance to Disinfectants

• prions
• bacterial spores
• Coccidia (Cryptosporidium)
• Mycobacterium
• nonlipid viruses
• (e.g. hep A, polio, adeno)
• fungi
• rickettsiae, chlamydiae
• vegetative bacteria
• lipid-containing viruses
• (e.g. HIV, herpes, flu)

4
Properties of Ideal Disinfectants

• Broad spectrum (kills everything)
• High efficiency (kills rapidly)
• Unaffected by organic matter, soaps detergents,
  water hardness, pH
• Nontoxic, non-corrosive, nonflammable
• Odorless
• Cheap
• Stable
• Environmentally friendly

5
Types of Disinfection

• Chemical
• Physical
• Thermal (heat)
• Filtration
• Radiation

6
Chemical Disinfectants

• Chorine
• Iodine
• Alcohol
• Phenolics
• Quaternary ammonium
• compounds
• Glutaraldehyde
• Formaldehyde
• Hydrogen Peroxide
• Chlorhexidine

7
Misconception 1

• Bleach does it all!

As long as all my labs use bleach for routine
disinfection, theyre safe.
8
Chlorine

• Available in liquid, powder or tablet form
• Household bleach usually 5-6 Na hypochlorite
• In-use dilutions depend on application and amount
  of organic material present
• general disinfection - 5,000 ppm Av Cl (10
  bleach)
• organic material - 10,000 ppm Av Cl (20 bleach)
• Corrosive neutralized by organic material
• Effective vs veg. bacteria, mycobacteria,
  viruses, and fungal spores, and has some
  sporicidal activity
• Working solutions should be prepared fresh
  (within 24 hours) and kept in light-protected
  containers
• ClO2 gas used in mail center against anthrax

9
Misconception 1 Correction

• There aint no panacea!
• Bleach is a good high-level general disinfectant
  but doesnt kill everything under normal
  conditions of usage
• 10-20 solution, limited contact time, organics
• Given adequate CT, it might almost be a sterilant
  but process would be impractical
• There are always

the prions
10
Misconception 2

• 70 ethanol or IPA is the best routine
  disinfectant for biosafety cabinets.

Its cheap, effective, safe and leaves little
residue.
11
Alcohols

• Typically ethyl or isopropyl alcohol
• 70 in water is most effective concentration
  100 alcohol is not effective!!!
• Effective against enveloped viruses and
  vegetative bacteria longer contact times (10
  minutes) required for activity against fungi and
  mycobacteria variable activity against
  non-enveloped viruses no activity against
  bacterial spores
• Longer contact times difficult to achieve due to
  loss by evaporation

12
Is Ethanol Safe?

• and how about ethanol toxicity?

13
Misconception 2 Correction

• 70 EtOH or IPA is a pretty good disinfectant for
  routine BSC use but
• its not effective against spore-formers and
  marginally effective vs MTB, fungi and
  non-enveloped viruses
• its flammable as a liquid and nearly explosive
  as a spray, and burns with an almost invisible
  blue flame but then again, you shouldnt be
  using an open flame in a BSC anyway, right?
• Watch toxicity issues when in frequent use

14

• So what are some effective alternatives?

15
Phenolics

• Wide variety of phenolics available generally
  used in combination with detergents
• Effective against enveloped viruses vegetative
  bacteria variable activity against fungi and
  mycobacteria, depending on product limited
  activity against non-enveloped viruses no
  activity against bacterial spores
• Disadvantages include toxicity, neutralization by
  hard water and a pungent, unpleasant smell
• Not easily neutralized by organic material and
  non-corrosive
• Vesphene, Hil-Phene, LpH

16
Glutaraldehyde

• 2-4 aqueous solution, often with activator
• Broad spectrum antimicrobial activity, including
  non-enveloped viruses and mycobacteria (20 min),
  and bacterial spores (3 hours)
• Very effective cold sterilant commonly used to
  disinfect endoscopes
• Activated product has limited shelf-life
• Controversial product because of adverse health
  effects including mucous membrane irritation,
  contact dermatitis, occupational asthma
• Cidex taken off the UK market May 2002

17
Formaldehyde

• Supplied as solid paraformaldehyde (flakes or
  tablets), or as liquid formalin (37 solution of
  formaldehyde in water containing 100 ml/l of
  methanol as a stabilizer)
• Disinfectant use is typically 4
• Broad spectrum of activity against all classes of
  microorganisms
• Less susceptible to inactivation by organic
  material
• Corrosive, caustic, irritant, carcinogen
• Can be neutralized with ammonium hydroxide

18
Hydrogen Peroxide
.

• Available as a concentrated 37 solution in water
  (6 in-use solutions) and with peracetic acid
  (Spor-Klenz, Decon-Spore 200 Plus)
• Effective against vegetative bacteria,
  mycobacteria, fungi, viruses and spores
• Main incompatibility is with natural rubber
  products
• Leaves no residue (2H2O2 --gt 2H2O O2)
• Vapor phase hydrogen peroxide (VHP) is good
  volume disinfectant (35-37 solution is converted
  to vapor phase by heat)
• Accepta 8101 is a water biocide based on stable
  combination of H2O2 and silver ions - prod lit
  indicates high levels of wide-spectrum activity
  http//www.accepta.com/Industry_Water_Treatment/Bi
  ocide_H2O2_Ag.asp

19
Misconception 3

• Nucleic acid extraction methods do not reduce
  sample infectivity.

Extracted materials still need to be handled as
infectious.
20
It Aint Necessarily So

• Do nucleic acid extraction methods disinfect?
• Usual answer - maybe not or probably not
• J.A. Blow and colleagues tested two common
  extraction techniques - TRIzol LS Reagent
  (Invitrogen) and AVL Buffer (Qiagen) - against
  alpha-, flavi-, filo- and bunyaviruses

21
The Results Please, Maestro

• No plaques were detected in any extraction
  reagent plus virus combination therefore, the
  extraction reagents appeared to inactivate
  completely each of the high-titer viruses used in
  this study. These results support the reliance
  upon either TRIzol LS Reagent or AVL Buffer to
  render clinical or environmental samples
  non-infectious.

22
Misconception 3 Correction

• It would appear that at least some extraction
  procedures may disinfect extraction samples
• Virus test panel limited but common practice has
  been to accept data as indicative of disinfection
• For other procedures that dont involve known
  disinfectants (such as guanidine HCl at gt4M), the
  best response is still probably not - be safe.

23
Physical Disinfection Approaches

• Radiation
• microwave - destroys protein structure alt.
  medical waste treatment expensive
• ultraviolet (UV) - requires direct exposure
  effect decreases rapidly with distance dangerous
• ? irradiation - good penetration effective
  expensive
• Incineration
• destroys matrix not socially acceptable
  expensive exhaust concerns regulated
• Filtration
• No good on solids
• HEPAs are very effective for air wide range of
  effective choices for liquids matrix preserved

24
Misconception 4

• I only need to keep my BSC clean - the UV lamp
  will keep it disinfected.

Why risk corrosion from bleach and fire from
alcohol if I dont need to?
25
Effects of UV

• UV is between visible light and x-rays
• UVA (380315 nm, Long Wave or "blacklight)
• UVB (315280 nm, Medium Wave), and
• UVC (lt 280 nm, Short Wave or "germicidal)
• UV at ?254 nm causes thymine dimers in DNA
  molecules, rendering them non-functional and
  preventing replication of microorganisms
• Must exceed a threshold because normal mammalian
  cells have a mechanism that repairs thymine
  dimers.

26
Misconception 4 Correction

• Output of UV lamp is often reduced by dirt and
  dust buildup, and bulb degradation.
• Some surface areas may be protected from UV
  exposure by items in the BSC either covering or
  shadowing those areas.
• When was the last time you saw an operator
  actually empty the BSC completely after work?
• UV damages a microbes DNA but doesnt actually
  kill or inactivate the agent so dimer repair and
  shielding by dirt and other agents may leave
  viable material.

27
Is There A Bottom Line Here?

• Since there is no panacea, and even sterilants
  have their limitations, each use of a
  disinfectant requires a
• RISK ASSESSMENT
• Spills, response kits, even individual labs,
  deserve this to ensure that the disinfectants
  available for use are effective against the
  agents anticipated or in use.