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Determining the aetiological diagnosisThis section clarifies the microbial aetiology based on clinical, radiological, and laboratory evidence, emphasising the complexities of assigning causation.
Clinical featuresClinical manifestations of bacterial, atypical bacterial and viral pneumonia frequently overlap and therefore may not reliably distinguish between the various aetiologies. An ill child with high fever, marked tachypnoea, myalgia, and localised auscultatory findings commonly indicates a bacterial cause 3,4 . In contrast, a child with lowgrade fever, runny nose, wheezing and bilateral, diffuse lung signs point more towards a viral cause 4 . Wheeze is common with viral or atypical bacterial pneumonia (Mycoplasma pneumoniae and Chlamydophila pneumoniae). In Mycoplasma infection, commonly the symptoms appear gradually with initial pharyngitis. Subsequent hoarseness and intractable cough indicates extension of the infection into the lower airways. Symptoms are milder than with other bacterial pneumonias and it is thus called "walking pneumonia". Although the cough is initially dry, it later becomes productive 5 . Children are more susceptible to get mycoplasma pneumonia. It has been reported in 10 to 40% of CAP among children, more common in older than younger children 6 . Coryza is unusual. However, in younger children less than five years, coryzal symptoms may be present 5 . On auscultation of the chest, scattered or localised rales and expiratory wheezes may be found. Consolidation is uncommon. Extrapulmonary manifestations such as arthritis, lymphadenitis, hepatosplenomegaly and haemolytic anaemia may also suggest mycoplasma infection 5 . However, these clinical features are not specific and can be found with Chlamydophila pneumoniae or viral infections as well 7 . Also, absence of these signs does not exclude mycoplasma infection.
Chest x-rayChest x-ray (CXR) may provide a clue to the aetiology. However, routine CXRs are not warranted for patients with suspected CAP.