Legionellosis is caused by the bacterium Legionella pneumophila and includes pneumonic form (Legionaires disease) and the non-pneumonic form (Pontiac Fever). Legionaires disease presents as pneumonia, with a dry non-productive cough and severe flu-like symptoms. It can occur sporadically as an uncommon cause of community-acquired pneumonia, or as cases associated with environmental sources such as hospitals, hotels and factories.

Influenza or 'flu' is a respiratory illness associated with infection by influenza virus. Symptoms frequently include headache, fever, cough, sore throat, aching muscles and joints.

Influenza occurs most often in winter and usually peaks between December and March in the northern hemisphere. There are two main types that cause infection: influenza A and influenza B. Influenza A usually causes a more severe illness. The influenza virus is unstable and new strains and variants are constantly emerging, which is one of the reasons why the flu vaccine should be given each year.

Tuberculosis (TB) is an infectious disease caused by the bacteria Mycobacterium tuberculosis, which is spread by airborne droplets. The risk of infection depends upon duration of exposure, the instensity of the exposure, and the immune status of the person exposed. The immune system clears the bacteria immediately in more than 80% of people exposed. In a small proportion of people who have been infected, the bacteria are walled off and remain dormant but viable. This is called latent TB.