Legionellae action plan for health care facilities.



Planning and implementing preventive measures

Maintaining mechanical systems for the control of Legionellae is crucial for reducing the risk of Legionnaires' disease.

Evaluating the usefulness of environmental sampling

Officials at the CDC do not recommend conducting environmental sampling until a case of legionellosis has been confirmed. Once a case of Legionnaires' disease has been confirmed, however, the CDC recommends environmental sampling to find the source of the legionellae that caused it. Other experts disagree with this approach, preferring to conduct environmental sampling periodically even if no cases of legionellosis have been detected ("routine sampling"). Here is the gist of the debate over routine environmental sampling:

Routine sampling will benefit some hospitals more than others. Reviewing A-E below will help you decide what is best for your institution.

Does this mean sampling is useless? No. It is true that you cannot assess your risk of Legionnaires' disease based solely on environmental sampling results. But you do not need to know exactly what level of Legionellae or percentage of positive samples will cause Legionnaires' disease in order to make use of sampling results. You just want feedback on the condition of your water. Are our preventive measures working? Should additional control measures be implemented?

Thus sampling may help you decide how much money to spend on preventive measures. If results are consistently negative, you will still maintain your systems to prevent legionellae growth. But positive test results, depending on the legionellae counts and the areas sampled, may indicate that you need to do more. Say your hospital keeps hot water at 60C (140F) to control legionellae because you treat several high-risk patients. If you took samples and found high legionellae counts, you would know that the high-temperature water is not controlling legionellae. If samples were consistently negative and no cases of legionellosis occurred, you would assume that it is.

One screening will not tell you that the systems are legionellae-safe even if all samples test negative. One screening may, however, be enough to indicate that a problem exists. If, for example, you were to find more than 150 cfu/ml (colony forming units per milliliter) in all of 10 water samples collected from showers and faucets in a transplant ward, you would know with certainty that immediate corrective action is indicated.

But several screenings are usually required to make good decisions. For example, if 1 or 2 cfu/ml were found in 5 of 15 samples collected from faucets in low-risk patient areas, and the other10 samples tested negative, it would be difficult to decide what action to take, if any, based on only one screening. Thus test results are m ore accurately interpreted by viewing trends rather than snapshots, just as stock investors generally do better by analyzing 10-week averages rather than selecting a stock based only on its change from one week to the next.

In summary, environmental sampling normally will not give a simple yes-safe or no-unsafe answer, nor will it always tell exactly what action to take. Sampling results are merely information - information to help you make better decisions. This is the question you must answer for your institution: Is the information worth the cost?

What if you take corrective action (disinfect systems) based on environmental sampling results even if your institution would not have had any cases of Legionnaires' disease if no corrective action had been taken? You spend money unnecessarily.

Say you are in the witness chair and the plaintiff's attorney asks about your efforts to control legionellae. You explain your preventive measures and produce a file of maintenance records. But then the attorney asks, "What made you think your preventive measures were working when legionellae are not detected in the water system. Patients should be observed per CDC recommendations even if all environmental samples have tested negative.

Establishing communication between facility management,

infection control, and the medical staff

Ideally, the facility manager will be alerted whenever legionellosis is detected in patients so that he or she will know to investigate mechanical systems, and medical staff members will be alerted whenever environmental samples are positive so that they can be especially watchful for cases of legionellosis. Consider initiating communication by distributing a copy of the handout, "Legionnaires" Disease: information for physicians, nurses, and infection control practitioners" (appendix 1) to the appropriate staff.

Determining when to disinfect systems

A multitude of factors need to be considered before deciding whether or not to take corrective action, and if so, what action to take. Don't wait for the CDC or another agency to establish a strict set of "if this, do that" rules-they probably never will, because no stringent set of guidelines will fit every facility all the time. However, a base guideline is useful as a starting point for decision making.

A base guideline for the domestic water system

In conjunction with the important considerations listed below, the guidelines established by the Allegheny County (Pennsylvania) Health Department can serve as a starting point for deciding when to disinfect the domestic water system:

Consider disinfecting the domestic water system if (1) 30 percent or more of samples taken in any given screen test positive for legionellae, or (2) one or more samples in a screening, but fewer than 30 percent, test positive and the hospital has had prior cases of nosocomial legionellosis, or (3) a case of nosocomial legionellosis is confirmed.

Review these important considerations before applying the above guideline to a specific situation:

Review the criteria for interpreting the results of samples taken from areas occupied only by low-risk individuals (table 1). Also, note that New South Wales (Australia) has established 10 cfu/ml as the maximum allowable legionellae count in warm water systems.

A base guideline for cooling towers

Table 1.

Criteria for Interpreting Results of Samples

Taken from Areas Occupied only by Low-Risk Individuals

Legionellae per ml Cooling Tower Domestic Water
detectable but <1 A B
1 - 9 B C
10 - 99 C D
100 - 999 D E
1,000 + E E

A = Low level of concern.

B = The legionellae count represents little concern but indicates the system is a potential amplifier for legionellae.

C = Low but increased level of concern. Disinfection should be considered.

D = Uncommonly high levels. Approaching levels that may cause outbreaks. Disinfect systems.

E = Very high levels. Outbreak potential. Disinfect systems immediately.