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Listed below are answers to common background questions that reporters have about legionellosis. Contact CDC’s Media Relations office with additional questions.

Questions and Answers

Q: Is legionellosis (Legionnaires’ disease and Pontiac fever) reportable?

A: Yes, legionellosis is a nationally notifiable disease, so any case that is lab-confirmed should be reported to state health departments, which in turn notify CDC. However, not every case is immediately reported to CDC. The best source of information specific to individual cases or situations is the local or state health department where the patient lives or the outbreak is occurring. However, health departments usually release very limited information about cases in order to protect the privacy of those affected.

Q: Can CDC confirm if there are legionellosis cases in my state?

A: The best course of action is to contact your local or state health department for the most up-to-date information. Unless CDC has been contacted by the health department, we are unlikely to be immediately aware of local cases. However, we can answer questions about legionellosis in general.

Q: When does CDC get involved in responding to outbreaks of Legionnaires’ disease or Pontiac fever?

A: State and local health departments have jurisdiction over outbreaks in their state. States may invite CDC to assist with an investigation when additional expertise, capacity, or resources are needed. For information about a current outbreak, contact the state or local health department where the outbreak is occurring. For cruise ship outbreaks involving U.S. citizens and ports of call in the United States, CDC has jurisdiction over the response. Visit CDC’s Vessel Sanitation Program website for more information.

This graph shows reported legionellosis incidence (per 100,000 persons) in the United States from 1998-2012.

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This graph shows reported legionellosis incidence (per 100,000 persons) in the United States from 1998-2012. Beginning in 2003, there has been a general increase in the incidence of legionellosis. Factors contributing to this increase might include increased diagnostic testing or a true increase in disease transmission.

Q: How common is Legionnaires’ disease?

A: CDC estimates that between 8,000 and 18,000 people are hospitalized with Legionnaires' disease in the United States each year. However, only about 3,000 cases are reported to CDC each year.

For additional information about legionellosis, see CDC’s About the Disease website.

Q: Is Legionnaires’ disease on the rise?

A: In general, the number of cases reported to CDC has been on the rise over the past decade. This may reflect a true increase in the frequency of disease due to a number of factors (e.g., older U.S. population, more at-risk individuals, aging plumbing infrastructure, climate). It may also be a result of increased use of diagnostic testing or more reliable reporting to CDC.

During 2014, more than 4,500 U.S. cases of legionellosis (Legionnaires’ disease and Pontiac fever) were reported to CDC. This provisional case count is likely to change as numbers are finalized. These numbers are nearly identical to the provisional numbers at the end of 2013. Once finalized, there were almost 5,000 cases reported to CDC in 2013.

Q: Where does Legionnaires’ disease occur most often in the United States?

A: Legionnaires’ disease appears to be more common in the northeastern United States. Researchers are not certain why that is, but it is likely related to a combination of factors.

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