Recommendations

Key Recommendations

A patient with cough, fever, or any other suggestive symptoms may have COVID-19; consider testing for SARS-CoV-2.

Patient history and physical exam are important parts of the diagnosis and may elicit symptoms consistent with community-acquired pneumonia (CAP), immune defects, and/or potential exposure to specific pathogens. However, a definitive diagnosis of pneumonia requires the presence of a new infiltrate on chest x-ray (CXR).

History

The objective of history-taking should be to detect symptoms consistent with CAP, defects of immunity, and possible risk of exposure to specific pathogens.

Risk factors include age >65 years, residence in a healthcare setting, COPD, HIV infection, cigarette smoke exposure, alcohol abuse, poor oral hygiene, contact with children, and use of certain drugs (e.g., acid-reducing drugs, inhaled corticosteroids, antipsychotics, antidiabetic drugs, opioids). Diabetes mellitus and chronic liver disease or chronic kidney disease have also been associated with CAP.[79][80]

Clinical signs and findings of infection (fever or chills and leukocytosis) and respiratory symptoms (including cough, often with increasing sputum production, expectoration, dyspnea, pleuritic pain, and hemoptysis) are usually present. Nonspecific symptoms such as myalgia and arthralgia may be reported. In patients of advanced age, patients with chronic illness, and immunocompromised patients, the signs and symptoms of pulmonary infection may be less intense and the pneumonia may go unrecognized because of the presence of nonrespiratory symptoms.[81]

Some causes of pneumonia (e.g., legionellosis) may have a specific history. Legionellosis can present with headache, confusion, digestive manifestations such as diarrhea, and clinical manifestations of hyponatremia.

Mycoplasma pneumoniae infection is most common in young patients and patients who have been treated with antibiotics before their current presentation with pneumonia. It may present with extrapulmonary manifestations such as myringitis, encephalitis, uveitis, iritis, and myocarditis.[82]

CAP is more severe in males than in females, leading to higher mortality in males overall and especially those of older age.[83]

Physical exam

Perform a physical exam. The patient may be febrile, tachycardic, and breathless at rest. Auscultation of the chest may reveal crackles, rales, or bronchial breathing, and there may be presence of dullness on percussion or tactile vocal fremitus.

Early inspiratory crackles
Early inspiratory crackles

Auscultation sounds: Early inspiratory crackles

Imaging

Order a CXR as soon as possible in all patients admitted to hospital with suspected CAP to confirm or exclude the diagnosis. In general, performing a CXR is not routinely necessary in outpatients with suspected CAP. Posteroanterior and latero-lateral projections increase the likelihood of diagnosis of pneumonia and are useful in establishing the severity of the illness.[84]

The primacy of CXR in making the diagnosis of CAP has been challenged by studies using lung ultrasound and computed tomography (CT) scan of the chest. Consider ordering a lung ultrasound if the CXR is negative and the patient is older and frail or the clinical suspicion is uncertain.[85] The American College of Physicians recommends point-of-care ultrasound (POCUS) if there is diagnostic uncertainty in patients with acute dyspnea.[86] The American College of Radiology (ACR) further notes that POCUS has particular utility when access to CT is limited, either due to a need for rapid assessment or a critical condition that limits patient mobility and transportation to the radiology suite.[84]

Depending on availability, lung ultrasound may represent an easy and accessible technique for the diagnosis of CAP, and is an alternative imaging modality if the clinician has appropriate training and equipment. It is radiation-free, and its use is especially valuable when CXR is not available. The diagnosis of CAP via bedside lung ultrasound mainly depends on detecting consolidation. However, consolidation is not always present in CAP, because pneumonia may be interstitial or present as diffuse pulmonary infiltrations.[87] Evidence shows that lung ultrasound can diagnose pneumonia in adults with excellent accuracy, including in the emergency department.[88][89][90]​​​ One meta-analysis using CT as the criterion standard showed that ultrasonography was more accurate than chest radiography at diagnosing CAP.[91]​ The 2025 American Thoracic Society clinical guidelines state that for adults with suspected CAP, lung ultrasound is an acceptable diagnostic alternative to CXR in medical centers where appropriate clinical expertise is available.[92]

The utilization of chest CT may improve the diagnosis of CAP and can provide detailed information about the lung parenchyma and the mediastinum. However, the principal limitations include exposure to radiation, high cost, and the impossibility of bedside testing. One study has reported that in patients presenting to the emergency department with suspected CAP, early CT scan findings, when CT is used in addition to CXR, markedly affect both diagnosis and clinical management.[93] The ACR recommends that CT should be reserved for hospitalized, symptomatic patients with high risk factors, increased comorbidities and suspected complications, such as those with indeterminate findings on CXR, or suspected parapneumonic effusion or abscess.​[84]

Microbiology

The initial antibiotic treatment is empiric in most cases.[79]​ Determining the microbial etiology reduces inappropriate use of broad-spectrum antibiotics and helps to ensure appropriate antibiotic therapy, which is an important factor in reducing mortality. It also identifies resistant pathogens and pathogens that may have public health implications (e.g., Legionella).

Sputum and blood cultures:

  • Obtain pretreatment Gram stain and culture of lower respiratory secretions and blood cultures in the following patients in the hospital setting:[79][94]

    • Patients with severe CAP as defined by American Thoracic Society (ATS)/Infectious Diseases Society of America (IDSA) criteria for defining severe CAP (see Diagnostic criteria), especially if they are intubated.

    • Patients being empirically treated for methicillin-resistant Staphylococcus aureus (MRSA) or Pseudomonas aeruginosa.

    • Patients who have been previously infected with MRSA or P aeruginosa, especially those with a prior respiratory tract infection.

    • Patients who have been hospitalized and received parenteral antibiotics in the past 90 days.

  • These tests are not routinely recommended in other inpatients. Current IDSA/ATS practice guidelines consider diagnostic testing as optional for the patient who is not hospitalized or who is hospitalized with mild CAP.[94]​ Take into account local antimicrobial stewardship protocols, local etiologic factors, and the clinical presentation when deciding whether to obtain these tests.[79]

  • Sputum Gram stain is sensitive and highly specific for identifying the causative pathogens in patients with CAP. A meta-analysis found that this test is highly specific for identifying Streptococcus pneumoniae, Haemophilus influenzae, S aureus, and gram-negative bacilli. However, the proportion of false-negative results ranged from 22% (for H influenzae) to 44% (for S pneumoniae), indicating that a negative result does not conclusively confirm the absence of causative pathogens, and antibiotic therapy should not necessarily be stopped based on a negative sputum Gram stain.[95]​ Poor quality specimens also may provide misleading results and thus should be rejected. Endotracheal aspirates or bronchoscopically obtained samples may be required in the hospitalized patient who is intubated or unable to produce an adequate sputum sample.[94]

Pneumococcal and Legionella urinary antigen testing:

  • Test urine for pneumococcal antigen in patients with severe CAP. Test urine for Legionella antigen in patients with epidemiologic factors (e.g., association with legionella outbreak or recent travel) or patients with severe CAP.[94]​ Collect lower respiratory tract secretions for Legionella culture or nucleic acid amplification in patients with severe CAP at the same time. Urinary antigen testing has been associated with a reduction in mortality in large observational studies, and is important to consider given the increase in Legionella infections, especially among severely ill patients.[79]

Influenza virus testing:

  • There is a strong recommendation to obtain influenza virus testing during periods of community spread.[96]​ Test for influenza virus using a rapid influenza molecular assay (rather than antigen-based detection tests) when influenza viruses are circulating in the community. Testing may also be considered during periods of low influenza activity.[79]

Laboratory investigations

Order a complete blood count, blood glucose, serum electrolytes, blood urea nitrogen, and liver function tests in hospitalized patients. An elevated white cell count is suggestive of infection, while hematocrit and leukopenia are used as factors in severity scoring.[79][80]​​

Blood glucose, sodium and blood urea nitrogen are also used in severity scoring.[97][98]​ Chronic kidney disease and chronic liver disease are risk factors for mortality and complications in patients hospitalized with CAP.[79][80]

Measure arterial blood gases in severely ill or hospitalized patients. Oximetry is noninvasive and can be used continually.

Consider ordering additional biomarkers such as C-reactive protein (CRP) and procalcitonin (PCT), although the data on these markers is controversial. Initial PCT measurement is not recommended by the IDSA/ATS and has not been found to reduce antibiotic use among patients admitted to the emergency department.[99][100]

However, there is some evidence that these biomarkers may be useful for predicting inadequate host response. Do not order PCT without an established, evidence-based protocol.[101]​ The American College of Emergency Physicians and ATS/IDSA do not recommend the routine use of PCT when deciding on administration of antibiotics in the emergency department.[79][102]​​ High levels of CRP or PCT at initial presentation represent a risk factor for inadequate host response, whereas low levels are protective.[103] In patients with suspected pneumonia, a CRP level >10 mg/dL makes pneumonia likely.[104] Increased values of PCT are correlated with bacterial pneumonia whereas lower values are correlated with viral and atypical pneumonia. PCT is especially elevated in cases of pneumococcal pneumonia.[105][106]​​​​ Initial empiric antibiotic therapy should be started in patients with clinically suspected and radiographically confirmed CAP regardless of the initial serum PCT level.[79]

Consider pleural fluid aspiration and culture in all patients with a pleural effusion. Parapneumonic effusions are exudates; a positive Gram stain of pleural fluid indicates an empyema.[107]

Bronchoscopy

Consider bronchoscopy in immunosuppressed patients, in patients with severe CAP, and in cases of treatment failure. The most common sampling techniques are bronchoalveolar lavage (BAL) and protected specimen brushing (PSB). A threshold of 10⁴ colony-forming units (CFU)/mL in BAL samples indicates infection. For PSB, a threshold of 10³ CFU/mL has been recommended to distinguish colonization from infection.[108]​ Additionally, studies have shown that polymerase chain reaction (PCR) testing of the lavage sample may aid in diagnosis and management. One multicenter randomized controlled trial (RCT) showed that multiplex bacterial PCR exam of bronchoalveolar lavage decreased the duration of inappropriate antibiotic therapy in admitted patients with pneumonia and who were at risk of gram-negative rod infection.[109]

Molecular techniques

Routine bacterial cultures are too slow to be immediately therapeutically useful. Nucleic acid amplification tests such as PCR have improved diagnostic accuracy in CAP. Molecular techniques provide high sensitivity and specificity in the diagnosis of single or polymicrobial infections, and they can help to determine antimicrobial resistance (as may occur with Staphylococcus aureus, nonfermenting gram-negative bacilli, and Enterobacteriaceae) associated with severe CAP.[110]

Multiplex PCR has the ability to amplify more than one target sequence at a time, thus able to detect viral, bacterial, and/or other infectious agents in one reaction tube.[111]​ With high sensitivities and high specificities for identifying bacteria, especially S pneumoniae, multiplex PCR can be used to rapidly screen for multiple causative pathogens in a single reaction.[112][113]​​ Several multiplex panels contain Mycoplasma pneumoniae and Chlamydia pneumoniae as part of a comprehensive respiratory syndromic panel, as well as others designed for severe CAP that include Legionella pneumophila and M pneumoniae. Availability of multiplex PCR is laboratory specific, and clinicians should check with their laboratory for further details.[94]

The ATS recommends nucleic acid-based testing of respiratory samples for viral pathogens other than influenza only in hospitalized patients with suspected CAP who either have severe CAP or are immunocompromised, based upon the reported findings of high inpatient mortality associated with noninfluenza viruses in these vulnerable populations.[94][114]​​ Do not order broad respiratory pathogen panels unless the result will directly influence management decisions.[101]​

Routine use of nucleic acid-based testing is not recommended in outpatients with suspected CAP.[114]

Venepuncture and phlebotomy: animated demonstration
Venepuncture and phlebotomy: animated demonstration

How to take a venous blood sample from the antecubital fossa using a vacuum needle.

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