Atypical pneumonia

Overview 
Theory 
Diagnosis 
Management 
Follow up 
Resources 

Last reviewed: 22 Nov 2024

Last updated: 10 Sep 2024

Atypical pneumonia (non-COVID-19) is a community-acquired infection often seen in young adults or children living in close proximity.

Diagnosis is mostly clinical. Molecular-based diagnosis of nasopharyngeal swabs, throat swabs or sputum can be performed. Serology can be used to confirm the diagnosis.

Treatment is often outpatient based with a macrolide antibiotic or doxycycline.

Extrapulmonary manifestations may occur, especially in Mycoplasma pneumoniae infections.

Definition

Atypical bacterial pneumonia is caused by atypical organisms that are difficult to detect on Gram stain and difficult to culture using standard methods. The most common organisms are Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Legionella pneumophila. Atypical bacterial pneumonia generally is characterized by a symptom complex that includes headache, low-grade fever, cough, and malaise. Constitutional symptoms often predominate over respiratory findings. Although in most cases presentation can be in the milder spectrum of community-acquired pneumonia, some cases, especially if caused by L pneumophila, may present as severe pneumonia, necessitating intensive care unit admission. Other possible pathogens include other Chlamydophila species, Legionella species, Coxiella burnetii (Q fever), and respiratory viruses.

History and exam

Key diagnostic factors

age <50 years
persistent cough
dry cough
long duration of symptoms

Full details

Other diagnostic factors

recent community exposure
throat involvement
fever
headache
diarrhea
bullous myringitis
lung rales/crepitations
rash

Full details

Risk factors

close community settings
immunosuppression
cigarette smoking
chronic lung disease
travel
male sex
immunomodulating drugs

Full details

Diagnostic tests

1st tests to order

oxygen saturation in air
WBC count
hemoglobin
Liver function tests (LFTs)
BUN level
real-time reverse transcription polymerase chain reaction (RT-PCR) for SARS-CoV-2
chest x-ray

Full details

Tests to consider

urinary Legionella antigen
sputum culture
molecular diagnosis of Mycoplasma pneumoniae or Chlamydophila pneumoniae
nasopharyngeal PCR

Full details

Treatment algorithm

ACUTE

presumed atypical bacterial pneumonia: nonpregnant adult

presumed atypical bacterial pneumonia: pregnant or child

Contributors

Authors

Lorenzo Di Francesco, MD, SFHM, FACP

Professor of Medicine

Department of Medicine

Division of General Internal Medicine

Emory University School of Medicine

Disclosures

LDF is a Gen Medicine/Point of Care Editorial Board Member for ClinicalKey.

Peer reviewers

Mark Woodhead, BSc, DM, FRCP

Honorary Senior Lecturer (University of Manchester)

Consultant in General & Respiratory Medicine

Department of Respiratory Medicine

Manchester Royal Infirmary

Manchester

Disclosures

MW is an author of a reference cited in this topic.

Ethan Rubinstein, MD

H.E. Sellers Research Chair in Infectious Diseases

Head

Section of Adult Infectious Diseases

Department of Internal Medicine

Department of Medical Microbiology

University of Manitoba

Winnipeg

Canada

Disclosures

At the time of the peer review, Professor Rubinstein declared no competing interests. We were made aware that Professor Rubinstein is now deceased.

George L. Anesi, MD, MSCE, MBE

Assistant Professor

Medicine, Division of Pulmonary, Allergy, and Critical Care

Perelman School of Medicine

University of Pennsylvania

Disclosures

GLA receives research funding from the National Institutes of Health (K23HL161353), the CDC Foundation, the Society of Critical Care Medicine (SCCM), and the University of Pennsylvania Perelman School of Medicine Thomas B. McCabe and Jeannette E. Laws McCabe Fund. GLA reports payments for authoring chapters for UpToDate and for expert witness consulting, including involving COVID-19, and reports that his spouse is employed by the U.S. Food and Drug Administration (FDA).

Differentials
- Coronavirus disease 2019 (COVID-19)
- Typical bacterial pneumonia
- Viral pneumonia
More Differentials
Guidelines
- Diagnosis and treatment of adults with community-acquired pneumonia
- Guidelines for the management of community acquired pneumonia in adults
More Guidelines
Patient information
Pneumonia
More Patient information
Calculators
Community-acquired pneumonia severity index (PSI) for adults
CURB-65 pneumonia severity score
More Calculators
Videos
Tracheal intubation: animated demonstration
Bag-valve-mask ventilation: animated demonstration
More videos
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Atypical pneumonia

Summary

Definition

History and exam

Key diagnostic factors

Other diagnostic factors

Risk factors

Diagnostic tests

1st tests to order

Tests to consider

Treatment algorithm

presumed atypical bacterial pneumonia: nonpregnant adult

presumed atypical bacterial pneumonia: pregnant or child

Contributors

Authors

Lorenzo Di Francesco, MD, SFHM, FACP

Disclosures

Peer reviewers

Mark Woodhead, BSc, DM, FRCP

Disclosures

Ethan Rubinstein, MD

Disclosures

George L. Anesi, MD, MSCE, MBE

Disclosures

Differentials

Guidelines

Patient information

Calculators

Videos

Log in or subscribe to access all of BMJ Best Practice

Log in or subscribe to access all of BMJ Best Practice

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