There are many ways to develop pneumonia, ranging from inhaling toxic substances in the workplace to unknowingly being infected with bacteria in the hospital.
Any lung infection acquired outside of a hospital setting is considered community-acquired pneumonia (CAP).
Viruses and certain bacteria such as Streptococcus pneumoniae (S. pneumoniae), Haemophilus influenzae, and atypical bacteria, such as Chlamydia pneumoniae, Mycoplasma pneumoniae, and Legionella species, are among the most common culprits of CAP .
This article discusses the symptoms, causes, treatment, and prognosis of community-acquired pneumonia.
The clinical presentation of CAP varies enormously depending on the range. For example:
- Mild pneumonia characterized by fever and a productive cough.
- Severe pneumonia is characterized by difficulty breathing and sepsis.
CAP symptoms often develop rapidly and are accompanied by a rapid heartbeat, sweating, and a feeling of warmth. These are subjective signs that an infection is brewing.
The most common symptoms of CAP include:
- Shortness of breath
- Productive cough (cough with green or whitish phlegm)
- Fever and chills
- Chest pain that gets worse when you breathe or cough
- Pain in the upper abdomen (abdomen)
- Nausea and vomiting
The most common culprits of CAP are viruses, namely the flu virus and bacteria. Less commonly, fungi and parasites can trigger a lung infection.
Streptococcus pneumoniae is the most common bacterial cause of CAP, but other common germs include:
- Haemophilus influenzae
- Mycoplasma pneumoniae
- Chlamydia pneumoniae
- Gram-negative bacilli
- Staphylococcus aureus
Viruses can also cause CAPs. In fact, a viral infection, like the flu, puts you at a higher risk of getting bacterial pneumonia, which is often more serious. Besides the flu virus, the following viruses can also cause CAP:
If your healthcare provider suspects CAP, they’ll likely ask about your symptoms and perform a focused physical exam, listening to the heart and lungs for signs of infection.
They may also order a chest X-ray to look for signs of pulmonary infiltrates (such as pus or blood in the lungs).
Based on the high prevalence of CAP, the presence of pulmonary infiltrates on imaging, and the severity of your symptoms, broad-spectrum antibiotics may be initiated.
In mild to moderate cases, your healthcare provider may also prescribe the following to help inform their diagnosis:
- Blood cultures
- Gram stain and sputum culture
- Urinary antigen test for S. pneumoniae
- Search for Legionella spp.
- SARS-CoV-2 test
- Complete Blood Cell Count (CBC)
The type of treatment you receive largely depends on:
- The severity of your symptoms
- Presence of comorbidities
- Place where you receive treatment (inpatient or outpatient)
Viral CAP usually does not need antibiotics and resolves on its own with supportive treatment.
Antibiotics are the mainstay of treatment for bacterial CAP. Amoxicillin and doxycycline are preferred in people at low risk. Cures of 5 to 10 days are recommended for all people with CAP, with reassessment after treatment.
For people with CAP who do not have comorbid conditions or risk factors for drug-resistant pathogensmonotherapy (one drug treatment) with amoxicillin, doxycycline or a macrolide (azithromycin or clarithromycin) is recommended.
For people with CAP who have comorbiditiesguidelines recommend broader-spectrum coverage consisting of either monotherapy with a respiratory fluoroquinolone (levofloxacin, moxifloxacin, or gemifloxacin) or combination therapy with amoxicillin-clavulanic acid or cephalosporin plus a macrolide or doxycycline.
Choose the right antibiotic
The specific type of antibiotic you use will also be based on:
- Your allergy profile
- Previous use of antibiotics
- Bacterial resistance in the region
- Possibility of adverse effects
Anyone with CAP who has been recently exposed to one class of antibiotics should be treated with an antibiotic regimen involving a different class to avoid bacterial resistance. Healthcare providers will also collect data on bacterial resistance to MRSA and Pseudomonas to inform their bacteria choices.
Sputum (phlegm) cultures are only recommended in severe cases. Routine blood cultures, sputum cultures, and urinary antigen tests are not beneficial in people with non-severe CAP.
When to See a Health Care Provider
It can be difficult to suspect a CAP, especially if you are sick.
Studies show that people who receive treatment early fare much better than those who don’t. If you feel sick for more than a few days, do not improve with over-the-counter medications or antibiotics, or experience chest pain, a productive cough, or shortness of breath, seek immediate medical attention.
CAP is one of the leading causes of morbidity and mortality worldwide and the seventh leading cause of death in the United States, accounting for more than 4.5 million outpatient and emergency room visits annually. In fact, CAP is the second leading cause of hospitalization and the most common infectious cause of death in the United States.
The following risk factors, when present, increase your risk of morbidity and mortality:
- Advanced age
- Presence of pre-existing health conditions
- Smoking and alcohol abuse
- Living in crowded conditions, such as nursing homes and mass incarceration sites
- Have a medical condition that can impact the airways (such as stroke, seizure, anesthesia, drug or alcohol use, esophageal damage, or dysmotility)
- Weakened immune system, for example due to drug treatment or a medical condition such as diabetes, cancer or HIV
CAP has a highly variable outlook ranging from rapid recovery to life-threatening complications. Mortality associated with CAP is highly dependent on the clinical setting in which it is treated, ranging from 3% to 30% in most studies, and when therapy is initiated. Generally, the earlier antibiotics or antivirals are initiated, the better the prognosis.
Efforts to improve the outlook for people with CAP are primarily aimed at helping populations most at risk of mortality. Severe CAP is associated with significant mortality and, despite effective antibiotic therapy, between 16% and 36% of people with CAP may die in a short time.
Any lung infection acquired outside of a hospital setting is considered community-acquired pneumonia (CAP). The influenza virus and streptococcus pneumoniae are the most common viral and bacterial culprits, respectively.
A word from Verywell
CAP contributes significantly to mortality, especially in the sick and elderly. If you’re at high risk for CAP, it’s important to know the signs and symptoms to look out for to get the help you need.
Most cases of CAP are caused by viruses and do not require treatment with antibiotics. Completing your vaccination schedule as directed by a health care provider reduces your risk of CAP. Bacteria are less likely to cause CAP, but when they do, cases tend to be more severe. If bacteria are the cause of your CAP, antibiotics are the mainstay of treatment and it is imperative that you take your medications exactly as prescribed by your health care provider.