Letters to the Editor

Indian Pediatrics 2002; 39:1059-1061

Primary atypical pneumonia in children

M. Salaria and M. Singh have described and drawn our attention to the often-forgotten etiological agents of pneumonia in children, particularly Mycoplasma and Chlamydia(1). Although they rightly pointed out that Mycoplasma pneumoniae could affect "all age groups", its frequency in under-five children is usually not recognised(1). The main purpose of this note is to emphasize that M. pneumoniae is not a rare cause of pneumonia in preschool age and to point out some clinical clues in its diagnosis.

If we go by the criteria suggested for considering pneumonia as ‘atypical’, such as "patchy infiltrates on chest radiographs", "less virulent course", "lesser mortality than patients with typical pneumonia", "peripheral leukocytosis is less common" and "routine cultures fail to reveal a microbial cause"(1), then by far the commonest cause would be Respiratory Syncytial Virus (RSV) and not Mycoplasma or Chlamydia(2). In pneumonia caused by RSV radiologically demonstrated consolidation (typical pneumonia), especially segmental, as against patchy infiltrates (due to interstitial inflammation), are seen more often than generally believed(2). For these reasons, the terms ‘typical’ and ‘atypical’ are not very helpful in clinical pediatrics; instead what we must aim for is to detect or deduce the etiological agent causing pneumonia in every case. The decision to use an antimicrobial drug, and the choice of the drug, will be guided by the etiological agent most likely to have caused the pneumonia. Consequently even the terms ‘typical’ and ‘atypical’ pneumonia are not found in the lAP Textbook of Pediatrics(3).

The technically correct term is ‘primary atypical pneumonia’ and not merely ‘atypical pneumonia’. The word ‘atypical’ used as an adjective as in ‘atypical pneumonia’ can be subjectively applied to any pneumonia with some difference from what is ‘typical’, as the criteria listed above would indicate. Thus the term ‘atypical pneumonia’ need not be specific for etiology, but only for some clinical or radiological variation. On the other hand, ‘primary atypical pneumonia’ is specific for the etiologies suggested by the authors(1). In (adult) medical parlance, lack of response to penicillin was a major feature of ‘primary atypical pneumonia’ (typically Mycoplasma pneumonia, more recently Legionella pneumonia also), distinguishing it from penicillin-sensitive primary pneumonia (typically pneumococcal pneumonia). Pneumonias secondary to predisposing conditions, which may be immunological or anatomical, have more varied etiologies and they would not qualify for the term ‘primary atypical pneumonia’. For this reason the term ‘primary atypical pneumonia’ has relevance in adult medicine. In clinical pediatrics pneumonia caused by several agents, such as RSV, Parainfluenza Viruses, Mycoplasma, Chlamydia, Legionella etc. are not treatable with penicillin, and yet they are usually ‘primary’ (and not necessarily secondary to predisposing factors). If all of them could be included under ‘primary atypical pneumonia’, then such a term has little usefulness.

There are clinical and epidemiological clues for deducing at least some etiological agents in childhood pneumonia, either where laboratory support is inadequate or when it is unhelpful. For example, the causative microbes vary according to the age of the infant. In tropical Tamil Nadu, during The RSV season of September to December, most pneumonias in under-five children may be due to RSV(2). I will present some clinical clues for the diagnosis of pneumonia caused by M. pneumoniae as illustrated in a 4-year-old child who was under my care. This child had radiologically detected segmental consolidation in the right upper lobe and assuming pneumococcal aetiology, injection penicillin was started. Two days later he developed a skin rash, which was at first thought to be due to penicillin allergy. However, the rash evolved with pleomorphism, showing macular lesions of widely varying sizes, urticaria and also ‘target lesions’. Thus it was erythema multiforme, which is a relatively common feature of infection due to M. pneumoniae, as already mentioned by Salaria and Singh(1,4). The same day the child complained of left ear pain and on otoscopy, bullous myringitis (bullous of about 2×3 mm, with dark brown colour, on the tympanic membrane) was seen. This is another clinical clue, characteristic of M. pneumoniae disease(5). The cold hemagglutinin test was positive with a titre of 32 and later the M. pneumoniae complement fixation test was positive with 128 titre, together confirming the clinical diagnosis. This child had several important lessons to teach us, namely, M. pneumoniae can cause pneumonia in under-five children, it can cause radiological consolidation, and clinical clues such as erythema multiforme and bullous myringitis help us in deducing the correct etiology even at the bedside. Obviously, the lack of either clue does not speak against Mycoplasma etiology.

The cold hemagglutinin test may often be negative in under-five children with this infection, or be of low titre when present. Unlike what the authors have stated, it is not a bedside test. Blood should be drawn using syringe and collection tube that are warm and the blood should not be refrigerated before or during separation of the serum. If the blood is refrigerated, the hemagglutinins may get adsorbed on the red cells and the test loses its validity. The agglutination procedure should be done at 4º C. All these are not usually possible at the bedside.

In children beyond 5 years it is a relatively good test, which is neither ‘highly nonspecific’ nor ‘insensitive’ in the usual sense of these terms, unlike what the paper stated(1). The word ‘nonspecific’ is used for cold agglutinins in the sense that these antibodies are not directed towards the organism M. pneumoniae. Thus these antibodies are not organism-specific, and yet they are relatively specific as host response to M. pneumoniae infection. Anti-mycoplasmal antibodies, on the other hand, would be ‘specific’ for the organism. The phrase ‘highly nonspecific’ suggests that it is not at all reliable; on the other hand it is a good diagnostic test in healthy school age children with primary pneumonia caused by M pneumoniae. It suffers from lack of sensitivity usually only in preschool children, but in older children and adults its sensitivity is quite high.

In a study of the causes of pneumonia in under-three children in Papua New Guinea, Frank Shann and colleagues showed that 22 of 94 cases were caused by RSV, 5 of 74 by M. pneumoniae and 5 of 91 by C. trachomatis (6). Legionella pneumonia was not detected (6). Therefore, we must remember that all uncomplicated pneumonias in infants and preshool children are not caused only by pneumococcus or Hemophilus influenzae b, but as the authors have rightly taught us there are many more etiological agents to be borne in mind and diagnosed, for choosing the right remedies.

References

1. Salaria M, Singh M. Atypical pneumonia in children. Indian Pediatr 2002; 39: 259-266.

2. John TJ, Cherian T, Steinhoff MC. Etiology of acute respiratory infection in children in tropical southern India. Rev Infect Dis 1991; 13: S463-S469.

3. Balachandran A. Pneumonia in children. In lAP Textbook of Pediatrics (Ed) Parthasarathy A, Jaypee Brothers, New Delhi, 1999; pp 349-352.

4. Lyell A, Dick HM, Gordon AM. Mycoplasma and erythema multiforme. Lancet 1967; 2:1116.

5. John TJ, Fulginiti VA, McDonough G. Bullous myringitis and atypical pneumonia. J Amer Med Assoc. 1967; 201: 127.

6. Shan D F, Walters S, Pfifer LL. Pneumonia associated with infections with Pneumocystis, Respiratory Syncytial Virus, Chlamydia, Mycoplasma and Cytomegalovirus in children in Papua New Guinea. Brit Med J 1986; 292: 314-317.