Texas Recommendations for Sporadic Community-Acquired Cases

Only 15-20% of legionellosis cases reported to the CDC have occurred in outbreaks [13]. Most (80-85%) cases of Legionnaires' disease occur as sporadic, community-acquired pneumonias. Sporadic legionellosis is extremely difficult to study and determining the correct public health response to a single case is difficult. People are exposed to hundreds of potential water aerosols each week, and studies have suggested that, at least in a hospital situation, aspiration of potable drinking water may be an important route of transmission [26].

Most patients with Legionella infection have multiple potential exposures (workplace, hotel, or other public space) during their 10-day incubation period; it is almost always impossible to conduct a meaningful investigation around a single sporadic case.

A cluster of legionellosis cases with a common exposure can involve both Legionnaires' disease and Pontiac fever [65]. The Task Force therefore recommends that investigating health departments be alert to this possibility. Questions regarding ill contacts of Legionnaires' diseases case patients should not be limited to persons with symptoms of pneumonia.

The Task Force recommends the following guidelines to assist health department staff in responding appropriately to such events and to educate physicians on the importance of correctly confirming the diagnosis before informing a patient that they have Legionnaires' disease. The health department should disseminate information regarding Legionnaires' disease to physicians [eg, 66].


When a sporadic case of Legionnaires' disease is diagnosed, the first priority is to confirm the diagnosis. First, ensure that the patient has a compatible clinical syndrome. A patient must have x-ray confirmed pneumonia. Second, the case must be laboratory-confirmed. A positive culture or positive urine antigen test is necessary for a confirmed diagnosis of Legionnaires' disease. Single total antibody titers are not diagnostic and should never be used to confirm Legionnaires' disease.


I. Passive Case Detection and Follow-up
Cases of confirmed Legionnaires' disease reported by physicians or laboratories should be investigated by the local health department. (Confirmed cases should be reported to the local health department; 800-705-8868.) The patient or patient's contacts should be interviewed to ascertain all potential exposures to water or water aerosols at home, at work, and to obtain a travel history for the patient during the 10 days prior to onset with pneumonia symptoms. The DSHS case report DSHS IDEAS Form 5, 02/02; [Form], including the exposure information, should be sent to the Public Health Region office and the Texas Department of State Health Services promptly.

Family members, coworkers, and other contacts of the patient should be educated about Legionnaires' disease. Particularly emphasize that healthy children and adults have a low risk of acquiring the disease and the disease is not transmitted person-to-person. Remind contacts of the symptoms of Legionnaires' disease (nonproductive cough, high fever, anorexia, malaise, headache, myalgias, abdominal pain and diarrhea). Remind contacts that people who are immunosuppressed, organ transplant or bone marrow transplant recipients, cancer patients undergoing chemotherapy, or patients with chronic obstructive pulmonary disease are at increased risk.

Anyone experiencing symptoms should be evaluated by a physician. A fact sheet, entitled "Legionellosis: Legionnaires' disease and Pontiac fever," is attached as Appendix E. Local clinicians should be reminded to report patients who fit the case definitions.

II. Active Surveillance and Epidemiologic Investigation

If the local health department determines that two or more confirmed cases share a common reported exposure during any 6 month period, an epidemiologic investigation should be initiated. The investigation should include:

A. Case Finding
The local health department should promptly initiate case finding in the community.

1. Inform primary care physicians, emergency room staff, and radiologists in the potential outbreak area and any other locations necessary of the following:

a. That there is a cluster of legionellosis cases.
b. How a case of legionellosis is diagnosed.
c. Reporting requirements.

2. Contact local hospital infection control staff and emergency room staff to determine whether they have observed an increase in community-acquired pneumonia patients admitted to the facility.

3. Cultures, or sera, if remaining, should be requested to be sent to the public health laboratory and held appropriately.

B. Investigation
If there are 2 or more cases of Legionnaires' disease, interview patients or their proxies to learn more about their pertinent exposures.

C. Information Dissemination
Results of the health department investigation should be shared with participating physicians, hospitals, and health departments.

Environmental Testing

Environmental testing, in the context of legionellosis, is the sampling of water and plumbing structures of a facility's water distribution system.

I. Single Cases:

The findings of the local health department investigation should determine whether or not any environmental testing is indicated. Most individuals have too many potential exposures during a typical incubation period to make such testing meaningful. (If the patient was diagnosed using the urine antigen test and no culture is available to speciate and serotype, environmental assessments have extremely limited value.) However, in some instances the investigation may uncover residential or occupational exposures known to be associated with Legionnaires' disease cases. Environmental testing may be indicated in such cases.

II. Outbreaks

A. Any environmental exposures identified in the epidemiologic investigation that are significantly associated with disease transmission should be evaluated with environmental testing.

B. If patient culture isolates exist, these should be compared with environmental culture isolates by a reputable public health laboratory.