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Legionnaires' disease and aerosol infections            


Legionellosis (LEE-juh-nuh-low-sis) is a respiratory disease caused by Legionella bacteria. Sometimes the bacteria cause a serious type of pneumonia (lung infection) called Legionnaires' disease. The bacteria can also cause a less serious infection called Pontiac fever that has symptoms similar to a mild case of the flu.

Legionella are found naturally in freshwater environments, like lakes and streams. The bacteria can become a health concern when they grow and spread in human-made water systems, such as showers and faucets as well as cooling towers (air-conditioning units for large buildings). Home and car air-conditioning units do NOT use water to cool the air, so they are NOT a risk for legionella growth.

People can get Legionnaires' disease when they breathe in small droplets of water in the air that contain the bacteria. Less commonly, people can get Legionnaires' disease by aspiration of drinking water (when water "goes down the wrong pipe"). Most healthy people exposed to legionella do not get sick, but older people, current or former smokers, and people with weakened immune systems may be at increased risk. In general, people do NOT spread Legionnaires' disease and Pontiac fever to other people. More inforamtion about legionella can be found on the CDC's website.

Infections spread from person to person

Common colds

Common colds are the main reason that children miss school and adults miss work (adults have an average of 2-3 colds per year, and children have even more). A sore throat and runny nose are usually the first signs of a cold, followed by coughing and sneezing.

Viruses that cause colds can spread from infected people to others through the air and close personal contact. You can also get infected through contact with stool (poop) or respiratory secretions from an infected person. This can happen when you shake hands with someone who has a cold, or touch a doorknob that has viruses on it, then touch your eyes, mouth, or nose.

You can help reduce your risk of getting a cold by (1) washing your hands often with soap and water; (2) avoid touching your eyes, nose, and mouth with unwashed hands; and (3) staying away from people who are sick. There is no vaccine to protect you against the common cold.

You can protect others when you have a cold by (1) staying at home while you are sick; (2) avoiding close contact with others, such as hugging, kissing, or shaking hands; (3) moving away from people before coughing or sneezing; (4) coughing and sneezing into a tissue then throwing it away, or coughing/sneezing into your upper shirt sleeve, completely covering your mouth and nose; (5) washing your hands after coughing, sneezing, or blowing your nose; and (6) disinfecting frequently touched surfaces, and objects such as toys and doorknobs.  More information about common colds can be found on the CDC website.


Influenza (the flu) is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and sometimes the lungs. It can cause mild to severe illness, and at times can lead to death.

Most experts believe that flu viruses spread mainly by tiny droplets made when people with flu cough, sneeze, or talk. These droplets can land in the mouths or noses of people nearby. Less often, a person might also get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose, or possibly their eyes.

Anyone can get the flu (even healthy people), and serious problems related to the flu can happen at any age, but some people are at high risk of developing serious flu-related complications if they get sick (for example, people 65 years and older, people with certain chronic medical conditions, pregnant women, and young children).

The best way to prevent the flu is by getting a flu vaccine each year and practicing everyday preventive actions (like staying away from people who are sick, covering coughs and sneezes, and frequent handwashing) to help slow the spread of germs that cause respiratory (nose, throat, and lungs) illnesses. More information about the flu can be found on the CDC website.


Tuberculosis (TB) is caused by a bacterium called Mycobacterium tuberculosis. The bacteria usually attack the lungs, but TB bacteria can attack any part of the body. Not everyone infected with TB bacteria becomes sick. If not treated properly, TB disease can be fatal.

TB bacteria are spread through the air from one person to another. The TB bacteria are put into the air when a person with TB disease of the lungs or throat coughs, speaks, or sings. People nearby may breathe in these bacteria and become infected.

TB is NOT spread by shaking someone's hand, sharing food or drink, touching bed linens or toilet seats, sharing toothbrushes, or kissing. More information about TB can be found on the CDC website.

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