section_path: Cause
section_name: Cause
paragraph_text: Cause
  
  Pneumonia is due to infections caused primarily by bacteria or viruses and less commonly by fungi and parasites. Although more than 100 strains of infectious agents have been identified, only a few are responsible for the majority of cases. Mixed infections with both viruses and bacteria may occur in roughly 45% of infections in children and 15% of infections in adults. A causative agent may not be isolated in about half of cases despite careful testing. In an active population-based surveillance for community-acquired pneumonia requiring hospitalization in five hospitals in Chicago and Nashville from January 2010 through June 2012, 2259 patients were identified who had radiographic evidence of pneumonia and specimens that could be tested for the responsible pathogen. Most patients (62%) had no detectable pathogens in their sample, and unexpectedly, respiratory viruses were detected more frequently than bacteria. Specifically, 23% had one or more viruses, 11% had one or more bacteria, 3% had both bacterial and viral pathogens, and 1% had a fungal or mycobacterial infection. "The most common pathogens were human rhinovirus (in 9% of patients), influenza virus (in 6%), and Streptococcus pneumoniae (in 5%)."
  
  The term pneumonia is sometimes more broadly applied to any condition resulting in inflammation of the lungs (caused for example by autoimmune diseases, chemical burns or drug reactions); however, this inflammation is more accurately referred to as pneumonitis.
  
  Factors that predispose to pneumonia include smoking, immunodeficiency, alcoholism, chronic obstructive pulmonary disease, sickle cell disease (SCD), asthma, chronic kidney disease, liver disease, and biological aging. Additional risks in children include not being breastfed, exposure to cigarette smoke and other air pollution, malnutrition, and poverty. The use of acid-suppressing medications – such as proton-pump inhibitors or H2 blockers – is associated with an increased risk of pneumonia. Approximately 10% of people who require mechanical ventilation develop ventilator-associated pneumonia, and people with a gastric feeding tube have an increased risk of developing aspiration pneumonia. Moreover, the misplacement of a feeding tube can lead to aspiration pneumonia. 28% of tube malposition results in pneumonia. As with Avanos Medical 's feeding tube placement system, the CORTRAK* 2 EAS, which was recalled in May 2022 by the FDA due to adverse events reported, including pneumonia, caused a total of 60 injuries and 23 patient deaths, as communicated by the FDA. For people with certain variants of the FER gene, the risk of death is reduced in sepsis caused by pneumonia. However, for those with TLR6 variants, the risk of getting Legionnaires' disease is increased.