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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.
T. Jacob John,
439 Civil Supplies Godown
Lane,
Kamalakshipuram,
Vellore, TN, 632 002
E-mail: vlr_tjjohn@sancharnet.in
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