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BY Annerie Hattingh 26/08/09. Atypical Pneumonia. Introduction:. Pneumonia caused by atypical pathogens Typical pathogens usually includes: - Strep. pneumonia - Haemophilus pneumonia - Klebsiella pneumonia Does not respond to the usual antibiotics

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Atypical Pneumonia

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Atypical pneumonia l.jpg


Annerie Hattingh



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Pneumonia caused by atypical pathogens

Typical pathogens usually includes:

- Strep. pneumonia

- Haemophilus pneumonia

- Klebsiella pneumonia

Does not respond to the usual antibiotics

Causes a milder form of pneumonia (hence the term “walking pneumonia”)

Characterized by a more drawn out coarse of symptoms

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Legionella + SARS are exceptions to the above –

both can be very severe infections

Typical pneumonia can come on more quickly + with more severe early sx

The arbitrary classification of typical vs. atypical pneumonia is of limited clinical value

Literature now shows that a primary pathogen may co-exist with a secondary one, further blurring this distinction


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“Classical” atypical pneumonias:

1.) Mycoplasma pneumonia

2.) Chlamydia pneumonia

3.) Legionella pneumonia

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Other micro-organisms that cause similar patterns

of presentation:

1.) Chlamydia psittaci (exposure to birds)

2.) Coxiella burnetti (presenting as Q fever)

3.) Viral pneumonias - Influenza A



- Adenoviridae

- Varicella pneumonitis

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It is thought that the 3 main atypical pathogens might be implicated in up to 40% of CAP

The precise incidence is not known

Often not identified in clinical practice due to lack of readily available, reliable standardized tests to confirm dx

By age 20, 50% of people in the USA have detectable levels of Antibodies to Chlamydia


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Risk Factors:

Mycoplasma + Chlamydia spread by person-to-person contact

- spread most common in closed populations e.g.

schools, offices + military barracks

Legionellae found most commonly in fresh water + man-made H2O systems

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Risk Factors:

- sources of contaminated H2O includes:

* showers

* condensers

* whirlpools

* cooling towers

* respiratory equipment

* air conditioning systems

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Risk Factors:

Other risk factors include:

- young, healthy people

- cigarette smoking

- lung disease (like COPD)

- weakened immune system (e.g. chronic steroid

use or HIV)

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Mycoplasma pneumonia:

Gram neg bacteria with no true cell wall

Frequent cause of CAP in adults + children

Prevalence in adults with pneumonia 2 – 30%

Tends to be endemic, occurring @ 4-7yr intervals

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Mycoplasma pneumonia:

Clinical Features:

Symptomatic / asymp

Gradual onset (over few days – weeks)

Prodrome of “flu-like” symptoms

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Mycoplasma pneumonia:

Clinical Features:

Including: - headache

- malaise

- fever

- non prod. Cough

- sore throat

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Mycoplasma pneumonia:

Clinical Features:

Objective AbN on physical exam are minimal in contrast to the pt’s reported symptoms

Present like many of common viral illnesses BUT persistence + progression of sx help to mark it out

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Mycoplasma pneumonia:

Extrapulm. Manifestations/Complications:

Can involve: CNS, Blood, Skin, CVS, Joints, GIT

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Mycoplasma pneumonia:

Extrapulm. Manifestations/Complications:

Neurological compl.

Aseptic meningitis

Cerebellar ataxia

Transverse myelitis

Peripheral neuropathy

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Mycoplasma pneumonia:

Extrapulm. Manifestations/Complications:

Neurological manifestations are infrequent

Usually found in kids, if seen

Associated with increased morbidity + mortality

Antecedent resp. infection not always present

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Mycoplasma pneumonia:

Extrapulm. Manifestations/Complications:

Hematological compl.

Hemolytic anemia

IgM antibodies to erythrocyte membrane I antigen are present

Produces a cold agglutinin response that leads to hemolysis

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Mycoplasma pneumonia:

Extrapulm. Manifestations/Complications:

Dermatological compl.

Include rashes such as:

Erythema multiforme

Erythema nodosum


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Mycoplasma pneumonia:

Extrapulm. Manifestations/Complications:

Cardiac involvement:



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Mycoplasma pneumonia:

Extrapulm. Manifestations/Complications:

Joint involvent: (occationately described)



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Mycoplasma pneumonia:

Extrapulm. Manifestations/Complications:

GIT symptoms:

N + V


Pancreatitis (rarely)

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Genus Chlamydia includes 3 species that infect humans: - C. psittaci

- C. trachomatis

- C. pneumonia

Small, coccoid, Gram neg bacteria that resemble rickettsiae

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Chlamydia trachomatis - seen in newborn infants

during delivery

- has been ass. with

pneumonia in adults

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Chlamydia psittaci:

Ornithosis is a systemic infection often acc. by pneumonia

Common in birds + some domestic animals

Pet shop employees + poultry workers @ risk

Other systems involved: CNS (meningoencephalitis) + CVS (cult. neg. endocarditis)

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Chlamydia pneumonia:

Prevalence varies by yr + geographic setting

Causes 5-15% of all CAP

Repeat infection is common

Gradual onset which may show improvement before worsening again

Incubation 3-4 weeks

Initial non-specific URTI Sx lead to bronchitic/

pneumonic features

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Chlamydia pneumonia:

Most infected remains quite well + asymptomatic

Can cause prolonged, acute bronchitis with

prod. cough

Hoarseness + headache are common features

Fever relatively uncommon

Sx may drag on for weeks/months despite course of appropriate antibiotics

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Chlamydia pneumonia:

Clinical severity usually caused by a secondary pathogen or co-existing illness e.g. diabetes


Sinusitis, otitis media

New onset asthma after acute infection

Endocarditis, myocarditis

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Legionella pneumonia:

Aerobic, motile, non-encapsulated, Gram neg bacilli

Tends to be the most severe of the atypical pneumonias

Focal outbreaks centered around poorly maintained air conditioning / humidification systems

Incubation 2-10 days

Initial mild headache, myalgia leading to fever, chills + rigors

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Legionella pneumonia:

Minimally prod. cough

Dyspnoea, pleuritic pain + hemoptysis are not uncommon

Extra pulmonary legionellosis is rare but can be severe

CVS most common extrapulm. site causing myocarditis, pericarditis + endocarditis

Also pancreatitis, peritonitis, glomerulonephritis + focal neurological deficit

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CXR findings are usually non-specific and difficult to distinguish from other pneumonias

Chest signs on examination minimal

Rx of suspected atypical pneumonias should be empirical

Cultures + serologic tests are not routinely available in laboratories

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A 53yr old patient with severe

Legionella pneumonia.

CXR shows dense consolidation in both lower lobes.

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A 40yr old patient with Chlamydia pneumonia.

CXR shows multifocal, patchy consolidation in the right upper, middle and lower lobes.

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A 38yr old patient with Mycoplasma pneumonia.

CXR shows a vague, ill defined opacity in the left lower lobe.

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Severe cases should be admitted

Atypical pneumonias usually Rx as for other

CAP, at least initially

No evidence that routinely giving antibiotics active against atypical organisms leads to better outcomes in non-severe CAP

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Macrolides, such as Erythromycin, Clarithromycin + Azithromycin have been shown to be effective in the Rx of all 3 organisms

Erythromycin tends to be less well tolerated + only few trails demonstrates its efficacy in the Rx of Legionella

Severe Legionella infections may require rifampicin + a macrolide

Tetracycline, Doxycycline + Fluoroquinolones are also effective

Recommened duration of therapy usually 2-3 weeks

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Shakeel Amanullah: Atypical Bacterial Pneumonia; eMed. March 2008. Atypical Pneumonias; Jan. 2007. Encyclopedia – Atypical Pneumonia (Mycoplasma and Viral) (Walking Pneumonia); May 2008.

Rosen’s Emergency Medicine Online: Community Acquired Pneumonia

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