Influenza and pneumonia describe disease conditions of the respiratory system. Symptoms may include, but are not limited to, fevers, chills, cough, sputum production, malaise, runny nose, muscle aches and chest pain. Severe disease requires hospitalization. Influenza has a specific viral cause. Pneumonia has a number of possible causes.
Viruses
Influenza is a seasonal infection that causes malaise, fever, chills, sore throat, muscle aches, headaches, coughing and fatigue. It can also cause nausea and vomiting, but this is typically caused by gastrointestinal infections that are commonly referred to as "stomach flu." Many of the symptoms are caused by the body's reaction to the viral infection, according to "Harrison's Principles of Internal Medicine." Many viruses, including the influenza virus, are also responsible for causing pneumonia, which is an infection of the lung tissues. Some other viruses include parainfluenza, respiratory syncitial virus and adenovirus.
Bacteria
Bacteria are also responsible for causing pneumonias. According to "Current Medical Diagnosis and Treatment," some of these bacteria include Streptococcus pneumoniae and Staphylococcus aureus, Mycoplasma pneumoniae and Haemophilus influenzae. These bacteria can be inhaled in droplets from the environment or spread to the lungs from infections. The effects of the bacteria and the immune system's response to infection causes symptoms such as shortness of breath and impaired delivery of oxygen to the blood.
Fungi
Fungal pneumonia can occur in healthy persons, but are more likely to occur in those with compromised immune systems, such as HIV patients or those on immune suppressant drugs for organ transplants. Certain areas of the United States have a higher incidence of infection with particular fungal agents. For example, coccidioidomycosis, caused by Coccidioides immitis, is most common in the southwestern United States. Histoplasmosis is caused by Histoplasma capsulatum and is most common in the Mississippi River basin.
Chemical Agents
Certain chemical agents, if inhaled into the lungs, cause inflammation and an immune reaction that results in pneumonia. If a person has an altered mental status, such as from illness or drug intoxication, he is more likely to be unable to protect his airway from the inhalation of stomach contents in the case of vomiting, a process called aspiration. In such cases, stomach acid and other chemical contents damage the lungs and cause pneumonia.
Parasites
Various multicellular organisms, including worms, are a less common cause of pneumonia in the United States. Toxoplasma gondii is a parasite spread by cats and other animals. Strongyloides stercoralis, or threadworm, and Ascariasis, a roundworm, tend to infect animals, but can also cause intestinal and lung disease in humans.
Idiopathic
Idiopathic pneumonias describe lung damage, inflammation and characteristic symptoms of pneumonia with an unknown cause. In these cases, dysfunction of the immune system or a reaction to an unknown agent may be a causal factor.
References
- "Harrison's Principles of Internal Medicine"; Anthony S. Fauci; 2008
- "Current Medical Diagnosis and Treatment"; Stephen J. McPhee and Maxine Papadakis; 2010
