What do you understand by the term atypical pneumonia?

The answer

• The term "atypical pneumonia" is applied to non-lobar patchy or interstitial infiltrates on chest x-ray 
• The causative organism is not identified on gram stain or culture of sputum
• Often they are not toxic
• Do not have shivers and do not seek medical attention
• "Walking Pneumonia"

Is atypical pneumonia a 'community acquired pneumonia' or 'hospital acquired pneumonia' ?

The answer

• Community acquired pneumonia 

Which organisms are responsible for atypical pneumonia?

The answer

The pathogens causing atypical pneumonia include:

• Mycoplasma pneumonia

• Chlamydia psittaci

• Chlamydia pneumonia 

• Coxiella burnetii

• Francisella tularensis

• Legionella pneumophila

• Viruses including influenza A and B, parainfluenza, adenovirus and respiratory syncytial virus

What is the source of these infections? What is their habitat?

The answer

• Mycoplasma pneumonia / human

• Chlamydia psittaci / Birds

• Chlamydia pneumoniae /

• Coxiella burnetii /

• Francisella tularensis /

• Legionella pneumophila / Water

• Viruses including influenza A and B, parainfluenza, adenovirus and respiratory syncytial virus./ human

Describe the clinical picture (mode of presentation) of atypical pneumonia, mycoplasma pneumonia as an example.

The answer

• Commonly between 5-15 years

• Scratchy throat (tracheitis) 

• Refractory dry cough (bronchitis)

• Low grade fever

• Do not seek medical help

What are the physical findings of  atypical pneumonia?

The answer

• Not toxic

• No signs of consolidation

• Diffuse small airway obstruction

  • hyperinflation

  • prolonged expiration

• Bullae in tympanic membrane (bullous myringitis) in mycoplasma pneumonia

What are the radiological findings of atypical pneumonia?

The answer

• Patchy infiltrates

• Peribronchial thickening

• Interstitial pneumonia

• Hyperinflation

Describe morphological and cultural characteristics of mycoplasma pneumonia. 

The answer

• Mycoplasma pneumonia is one of the smallest free-living microorganisms

• It lacks a cell wall, and hence stains poorly on usual bacterial stains

• It grows aerobically and produces tiny colonies on special agar that have an "inverted fried egg" appearance

• Hemabsorption of red blood cells on the surface of agar plates is a feature of mycoplasma pneumonia

How does mycoplasma pneumonia produce the damage?

The answer

Pathogenesis 

• Mycoplasma pneumonia attaches to the cilia and microvilli of cells lining the bronchial epithelium

• Attachment is mediated by a surface adhesion, the P1 protein, which binds to oligosaccharides containing sialic acid in the bronchial epithelial cells

• Ciliary action is stopped followed by loss of cilia and desquamation of epithelial cells into the lumen

• Oligosaccharide receptors (1-F1) are not found in non-ciliated cells or mucus

Describe the pathological findings of mycoplasma pneumonia.

The answer

• Sloughing of cells into the lumen is responsible or the cough that defines the clinical presentation

• The inflammation conspicuously involves the interstitial space or alveolar wall with mono-nuclear cells

• The inflammatory process involves the trachea, bronchioles, and peribronchial tissues

• The lumen is filled with purulent exudate containing polymorphonuclear leukocytes 

• Bronchial and bronchiolar walls are infiltrated with monocytes and plasma cells

• There is widening of peribronchial septae and hyperplasia of type II pneumocytes

• Organisms are shed in respiratory secretions for 2-8 days after onset of symptoms, and shedding can continue for as long as 14 weeks after infection

Other pathogens producing atypical pneumonia produce similar pathologic changes.

How does our defenses respond to mycoplasma pneumonia?

The answer

Immunity to Mycoplasma pneumonias:

• Local and systemic specific immune responses occur

• IgA antibody wanes 2-4 weeks after onset of infection

• Complement-fixing serum antibodies peak at 2-4 weeks and disappear in 6 to 12 months

• Nonspecific immune response to the outer membrane also develop e.g., cold hemagglutinins (IgM antibodies that react with I antigen of human RBC’s)

• Immune mediated mechanisms play a role in M. pneumonia infection

• Reinfections is associated with quicker development of inflammatory changes in experimental animals

• High levels of IgG immune complex are found in the acute phase of illness and correlate with degree of pulmonary involvement

• M. pneumonia can stimulate B and T lymphocyte mitogenic activity

Do you get immunity for re-infection with mycoplasma pneumonia?

The answer

• Immunity to M. pneumonia is not complete, and re-infection is common

• Clinical disease is more severe in older children, suggesting that many clinical manifestations are due to cellular immune responses

How can we diagnose mycoplasma pneumonia?

The answer

Definitive diagnosis is made by the following:

• Isolation of the organism 

  • takes 2-3 weeks and is too expensive and time consuming

• Detection of M. pneumonia antigens or nucleotide sequences in clinical specimens by enzyme immunoassay or per DNA hybridization is under development

• Demonstration of an antibody response

  • the compliment fixation test detects specific antibody and is commonly used

  • antibody rises 7-9 days after infection, peaks at 3-4 weeks and lasts for 6-12 months

  • a four-fold rise or decline in titer is necessary for diagnosis

• Two thirds of patients with symptomatic M. pneumonia will develop high titers of cold agglutinins

  • these are not specific and are seen in other viral infections (adenovirus, EBV)

  • this test is simple and can be performed at the bedside

• New assays include indirect immunofluorescence and ELISA and detect IgM as well as IgG. An ELISA using adhesion PI protein is being developed.

Antigen detection and culture of sputum for specific pathogens helps establish the diagnosis in other cases of atypical pneumonia. Serology is useful but acute convalescent titers are needed. 

How do you treat mycoplasma pneumonia?

The answer

Therapeutic strategy:

• Erythromycin and tetracycline are equally effective in treatment of M. pneumonia infection

  • they shorten the course of infection but do not eliminate the carrier state

  • therapy is generally continued for 2-3 weeks, as relapses can occur in up to 10% cases

• Clarithromycin and azithromycin are also effective but much more expensive 

• Quinolones such as ciprofloxacin have in vitro efficacy against mycoplasma, but are expensive and contra-indicated in children

Can we use beta-lactum antibiotics to treat mycoplasma pneumonia?

The answer

• Since mycoplasmas lack a cell wall, beta-lactam antibiotics are ineffective for treatment

How can we prevent infections with agents causing atypical pneumonia?

The answer