Pneumonia is an infection of the alveoli (air sacs) and lower airways in the lungs that causes inflammation and fluid accumulation. There are two main types: community acquired pneumonia (CAP) and nosocomial pneumonia (acquired in the hospital). Many pathogens, including bacteria, fungi, and viruses, can cause pneumonia,^[1] but, in some cases, the cause cannot be identified.^[2]

Common signs and symptoms of pneumonia are shortness of breath, cough with or without mucus, chest pain, low blood oxygen levels, fever, chills, and fatigue. There may also be audible signs of fluid in the lungs, which a clinician can hear with a stethoscope. The severity of these signs and symptoms varies, ranging from mild respiratory distress to septic shock (characterized by a dangerous drop in blood pressure).

Certain populations have a different presentation of pneumonia. Younger children (<5 years) may be restless, vomit, have trouble eating, and show signs of breathing difficulties (e.g., nasal flaring, grunting, and chest retractions).^[3][4] In older adults (>65 years), signs and symptoms may be less noticeable and could include disorientation or delirium.^[1][5]

A pneumonia diagnosis is usually based on signs and symptoms in combination with chest imaging (e.g., X-ray or computed tomography) that shows signs of a lung infection. Since pneumonia presents similarly to other medical conditions, it is important to see a clinician for a diagnosis. A clinician will acquire a medical history and conduct a physical assessment to guide the choice of any necessary treatments, imaging, and/or blood tests. These tests will help rule out other possible causes of symptoms, like the flu, asthma, or pulmonary embolism.

Antibiotics are the first-line treatment for most cases of pneumonia. The choice of antibiotic, however, will depend upon the clinician weighing the risks and benefits of antibiotic therapy, the person’s medical history, and local epidemiological data (community outbreaks, microbe prevalence, etc.).^[1] If testing (e.g., blood and sputum cultures, nasal swabs) indicates the causative pathogen is not a bacteria, an antiviral (to fight viruses) or an antifungal (to fight fungi) may be given.

Corticosteroids are not indicated for use in people with uncomplicated pneumonia; instead, they are reserved for people whose pneumonia is exacerbating preexisting reactive airway disease (e.g., COPD), or who are critically ill (e.g., septic shock) and not responding to usual treatments. Moderate to severe cases of pneumonia may also require supportive treatments, such as oxygen therapy, IV fluids, blood pressure medications, and airway/breathing support. ^[6] Aerosolized antibiotics are sometimes used in hospital settings for ventilator-associated pneumonia, but there is no robust evidence to support their efficacy. ^[7]

Many supplements have been studied for pneumonia, but there is little evidence to support their efficacy. For instance, a meta-analysis found that Vitamin C was ineffective in treating or preventing pneumonia.^[8] Similarly, probiotics, specifically the strain Lactobacillus rhamnosus GG, failed to prevent ventilator-associated pneumonia.^[9]

Although there is some evidence that low levels of vitamin D (measured by plasma 25-hydroxyvitamin D3) are associated with an increased risk of bacterial pneumonia^[10], it’s unclear whether supplementation reduces this risk. Lastly, a randomized controlled trial found that N-Acetylcystine (NAC) supplementation, despite lowering markers of oxidative stress and inflammation, did not improve chest imaging results in people hospitalized with pneumonia.^[11]

Conversely, zinc supplementation is associated with a reduced risk of pneumonia in children,^[12] but adding zinc as an adjunct to antibiotic treatment in children who already have pneumonia does not improve time to recovery.^[13][14]

There is minimal evidence that diet affects pneumonia. A cohort study found that increased coffee, tea, oily fish, and fruit were associated with a reduced risk of developing pneumonia, while increased red meat intake was associated with an increased risk of developing pneumonia.^[15] Given that this is observational data, controlled studies are needed to better determine the relationship between dietary patterns and pneumonia. Regardless of dietary pattern, people with pneumonia must meet their daily nutritional needs, as severe malnutrition in both young children (<5 years) and older adults (>65 years) with pneumonia is associated with an increased risk of mortality.^[16][16] Some studies have also found that increasing energy and protein intake can improve health outcomes in people who are hospitalized for severe pneumonia.^[17][18]

Some research suggests that increased physical activity^[19] and sauna bathing^[20][21] are associated with a decreased risk of developing pneumonia. Another common treatment is chest physiotherapy, which involves manual techniques to help clear mucus out of the airways. However, most studies don’t find it very useful.^[22][23]

Many types of pathogens can cause pneumonia, such as:

• Bacteria: Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, Legionella pneumophila, and methicillin-resistant Staphylococcus aureus (MRSA)

• Viruses: Human rhinovirus, influenza A or B, coronavirus, and respiratory syncytial virus (RSV)

• Fungi: Pneumocystis jirovecii, Aspergillus spp., and Mucorales

The most prevalent causative microbes vary geographically. Viruses account for the majority of cases in children (<5 years)^[24], whereas bacteria and viruses account for most cases of pneumonia in adults. Fungal pneumonia is quite rare and usually occurs in people who are immunocompromised (e.g., cancer patients).^[1]

Pneumonia can also be caused by foods, liquids, or gastric contents inadvertently entering the lungs, a condition known as aspiration pneumonia.