Appendix 4-A - Interpretation of Legionella Culture Results from Cooling Towers

Appendix 4-A
 

Interpretation of Legionella Culture Results from Cooling Towers
Legionella Test Results in CFU/mL1
Response
No detection (< 20 CFU/mL) Maintain treatment program and Legionella monitoring in accordance with the maintenance program and plan.
For levels at ≥ 20 CFU/mL but < 1000 CFU/mL perform the following:

o Review treatment program.
o Institute immediate online disinfection2 to help with control
o Retest the water in 3 – 7 days.

  • Continue to retest at the same time interval until one sample retest result is < 20 CFU/mL. With receipt of result < 20 CFU/mL, resume routine maintenance program and plan.
  • If retest is ≥ 20 CFU/mL but < 100 CFU/mL, repeat online disinfection2 and retest until < 20 CFU/mL attained.
  • If retest is ≥100 CFU/mL but < 1000 CFU/mL, further investigate the water treatment program and immediately perform online disinfection 2. Retest and repeat attempts at control strategy until < 20 CFU/mL attained.

o If retest is ≥ 1000 CFU/mL, undertake control strategy as noted below.

 

For levels ≥ 1000 CFU/mL perform the following:

o Review the treatment program and provide appropriate notifications per section 4-1.6 of this Subpart.
o Institute immediate online decontamination3 to help with control
o Retest the water in 3 – 7 days.

  • Continue to retest at the same time interval until one sample retest result is < 20 CFU/mL. With receipt of result < 20 CFU/mL, resume routine maintenance program and plan.
  • If any retest is ≥ 20 CFU/mL but < 100 CFU/mL, repeat online disinfection2 and retest until < 20 CFU/mL attained.
  • If any retest is ≥ 100 CFU/mL but < 1000 CFU/mL, further investigate the water treatment program and immediately perform online disinfection.2 Re-test and repeat attempts at control strategy until < 20 CFU/mL attained.
  • If any retest is ≥ 1000 CFU/mL:
    •  carry out system decontamination4.
1 Colony forming units per milliliter.

2Online disinfection means – Dose the cooling tower water system with either a different biocide or a similar biocide at an increased concentration than currently used.

3 Online decontamination means – Dose the recirculation water with a halogen-based compound (chlorine or bromine) equivalent to at least 5 milligrams per liter (mg/L) or parts per million (ppm) free residual halogen for at least one hour.

4 System decontamination means – Maintain between 5 to 10 mg/L (ppm) free residual halogen for a minimum of one hour; drain and flush with disinfected water; clean wetted surface; refill and dose to 1 – 5 mg/L (ppm) of free residual halogen and circulate for 30 minutes. Refill, re-establish treatment and retest for verification of treatment.
For chlorine treatment the pH range should be 7.0 to 7.6; for bromine treatment the pH range should be 7.0 to 8.7. At higher pH values the treatment times may need to be extended.

NOTE: Stabilized halogen products should not be used for online decontamination or system decontamination as defined in this Appendix per footnotes 3 and 4.

 

Effective Date: 
Wednesday, July 6, 2016
Doc Status: 
Complete
Statutory Authority: 
Public Health Law, section 225(5)(a)