Atypical pneumonia

Atypical pneumonia

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Atypical Pneumonia

What is pneumonia?
An acute infection of lung parenchyma including alveolar spaces and interstitial tissue. It can be caused by a lot of different micro-organisms such as viruses, bacteria, fungi and parasites and corrosive or toxic gases from a fire.

What is typical pneumonia?
Typical pneumonia refers to pneumonia caused by following etiological agents.

Etiological agents:

1. Common agents
- S. pneumoniae - most common cause of community-acquired bacterial pneumonia
- H. influenzae
- K. pneumoniae

2. Uncommon agents
- S. aureus
- S. pyogenes
- P. aeruginosa
- N. meningitidis

3. Rare agents
- Y. pestis
- B. pseudomallei
- Acinetobacter calcoaceticus

What is atypical pneumonia?
Atypical pneumonia refers to pneumonia caused by following etiological agents.

Etiological agents:

Bacteria
- Mycoplasma pneumoniae - most common agent
- Legionella sp. (Legionnaire's disease)
- Francisella tularensis (tularemia)
- Bacillus anthracis (anthrax)
- Chlamydia psittaci (psittacosis)
- Chlamydia trachomatis
- Chlamydia pneumoniae
- Coxiella burnetii (Q fever)

Viruses
- Influenza
- Parainfluenza
- Respiratory syncytial virus
- Adenovirus

Fungi
- Histoplasma capsulatum (histoplasmosis)
- Coccidioides immitis (coccidioidomycosis)

Atypical pneumonia has been commonly associated with milder form of signs and symptoms but pneumonia due to Legionella, can be quite severe and lead to high mortality rates.

Mycoplasme pneumonia

M pneumoniae is the most common agent causing atypical pneumonia and infections follow epidemic patterns. The periodicity of the outbreaks is from 4 to 8 years. Thus it is difficult to gauge the actual frequency of the infections.

One of the main reasons for the difficulty in identifying M pneumoniae in sporadic cases is the variability of available laboratory methods and the challenge in confirming the suspected infection. Most hospital laboratories do not attempt to culture the organism; thus, most diagnoses are made serologically, with an answer not becoming available until well after the patient has recovered.

Pathophysiology: The responsible organism, M pneumoniae, is a pleomorphic organism that lacks a cell wall. The prolonged paroxysmal cough seen in this disease is thought to be due to the inhibition of ciliary movement, since the organism has a filamentous end that allows it to slip between cilia within the respiratory epithelium.

Microscopically, it produces interstitial pneumonitis, bronchitis, and bronchiolitis. Peribronchial areas are infiltrated with plasma cells and small lymphocytes; within the bronchial lumina are neutrophils, macrophages, fibrin strands, and epithelial cell debris.

How do you get mycoplasma pneumonia infection?
Anyone in contact with a secretion (such as phlegm) from the respiratory passages of an infected person risks contracting the mycoplasma organism. However, close contact is required for transmission, more commonly found among members of the same family and in schools and day-care institutions. There is little point in isolating someone infected with the virus since some people carry the infection without feeling ill.

Contagious period:

The contagious period is probably fewer than 10 days and occasionally longer.

Sings and symptoms:

Typical symptoms include

-chills
-fever
-cough - may be dry or productive of phlegm
-bronchitis
-sore throat
-headache
-tiredness
-loss of appetite (anorexia)
-rash
-confusion (especially with Legionella)
-diarrhea (especially with Legionella)

Infections of the middle ear (otitis media) also can result.

Symptoms may persist for a few days to more than a month.
Unlike typical pneumococcal pneumonia, this disease progresses gradually.
Acute symptoms usually persist for 1 to 2 wk followed by gradual recovery, although many patients continue to have constitutional symptoms with fatigue and malaise for several weeks.

However, some patients have severe pneumonia, sometimes causing the adult respiratory distress syndrome
Extrapulmonary complications are
-hemolytic anemia,
-thromboembolic complications,
-polyarthritis, or
-neurologic syndromes, such as meningoencephalitis, transverse myelitis, peripheral neuropathies, or cerebellar ataxia.

Chlamydia pneumonia

Chlamydia pneumonia occurs year round and accounts for 5-15% of all pneumonias. It is usually mild with a low mortality rate.

Legionella pneumonia

It accounts for 2-6% of pneumonias and has a higher mortality rate.

High risk group:
-Elderly individuals
-Smokers
-People with chronic illnesses
-Weakened immune systems

Diagnosis:
Atypical pneumonia is usually diagnosed on the basis of typical symptoms.

Depending on the severity of illness, additional studies, such as a complete blood count, blood cultures, and sputum cultures, may be obtained.

Chest XRay
Fine patchy interstitial or perihilar infiltrates
Lower lobe more commonly affected

When certain forms of atypical pneumonia are suspected, certain tests may be ordered.
-Legionella antigen legionella pneumonia

Mycoplasma and Chlamydia pneumonia
-throat swabs
-blood tests for antibodies to Mycoplasma and Chlamydia

Treatment:
Treatment for atypical pneumonia is antibiotic therapy. Antibiotics may be needed for 10 - 14 days.
Effective antibiotics are
-erythromycin,
-azithromycin,
-clarithromycin,
-fluoroquinolones
-tetracyclines (Avoid in age >8 years or pregnancy)
-doxycycline (Avoid in age >8 years or pregnancy)

Mild cases- oral antibiotics may be appropriate.

Severe cases (especially in Legionella pneumonia) may require intravenous antibiotics and oxygen supplementation.

Prevention
There are no proven methods for preventing the atypical pneumonia.

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