Infection caused by the bacterium Streptococcus pneumonia, which is spread through contact with respiratory droplets from a person who is infected with or carrying the bacteria. The bacteria are a major cause of common illnesses, such as inflammation of the sinuses (sinusitis), but can also result in life-threatening infections, including meningitis and pneumonia. People with weakened immune systems, including people with HIV, are at higher risk for bacterial pneumonia, including Streptococcus pneumonia infection, than people with healthy immune systems.