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Brief Reports Indian Pediatrics 2001; 38: 157-160 |
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Mycoplasma pneumoniae Antibodies in Children with Acute Respiratory Infection |
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Mycoplasma pneumoniae, an important cause of upper and lower respiratory infections (LRI) in children, is resistant to b-lactam antibiotics that are frequently used in the treatment of LRI(1). This infection is prevalent world over with prevalence rates as high as 50% in some groups of children(1). From India, data on this infection are limited. A few recent studies show a high prevalence among children(2,3). There is no fully reliable and practical diagnostic test for this infection. Since culture is cumbersome, expensive and lacks sensitivity(4) and PCR is not practical for routine use in many developing countries, IgM specific ELISA is recommended as the single most appropriate test for the diagnosis of actue M. pneumoniae infection(4,6). We used this test to determine the frequency of M. pneumoniae infection in children with selected acute respiratory infections.
Children with pharyngitis, pneumonia or wheeze associated acute respiratory infection (WARI) attending the out patient clinic or admitted to the wards of one of the two pediatric units of our hospital were pros-pectively enrolled into the study from August to December 1998. Pharyngitis was diagnosed when the child had throat pain and redness, with or without exudates. Clinical evidence of LRI using WHO criteria(7), but without wheeze was considered pneumonia. Children with cough or rhinorrhea and fever followed by wheezing were classified as having WARI. All children were examined by a pediatrician and clinical data collected in a standard case report form. Chest X-rays were performed at the discretion of the attending physician but the data was not used as a part of diagnostic criteria. Blood was collected form children at presentation to the out patient clinic or shortly after admission to the ward. Sera were separated, stored at –20°C and tested in batches. Cold agglutination test (CA) was done according to standard procedure(8). Particle agglutination test (PAT) was done using gelatin particles coated with myco-plasma antigen (Serodia-Mycoll, Fujirebio Inc, Japan) following manufacturer’s instructions. IgM antibodies against M. pneumoniae were detected using a commercially available kit (Novum Diagnostica, Germany), following manufacturer’s instructions. Optical densities above the cut off as recommended by the manufacturer were considered positive. Data was entered in and analyzed using Microsoft Excel software. The study focussed only on the prevalence of M. pneumoniae infection in children. Tests for viruses and other bacteria were not done because of financial constraints. Treatment was initiated at the discretion of the attending physician.
A total of 92 children, 37 with pneu-monia, 40 with WARI and 15 with pharyngitis were included in the study. IgM antibodies were detectable in 30%, 28% and 40%, respectively (Table I). Overall, 28 (30.4%, 95% CI: 21.7 - 40.4) of the 92 children had IgM antibodies.
There was no difference in the clinical presentations of children who were IgM antibody positive compared to those negative. Most children presented with fever and cough of less than one-week duration. Nineteen (29.2%) of the 65 children who were less than five years old, were IgM positive compared to nine(33.3%) of the 27 children above this age. Comparison of results obtained using PAT and CA with that obtained using ELISA is presented in Table II. On testing 46 sera with erythrocytes obtained from a different individual, seven (15%) showed a difference of two dilutions or more in CA. Only two of the 13 samples negative by CA were positive either by ELISA or PAT.
Thirty per cent of the children with ARI enrolled in the study had IgM antibodies to M.pneumoniae. Although earlier studies from India showed lower prevalence of M. pneumoniae(9) our data is in agreement with more recent studies from India(2,3) and showed a high rate of M. pneumoniae infection among children with acute LRI (with or without wheeze). M. pneumoniae as reported in literature, was found to be associated with pharyngitis also. However, the numbers included in this group was very small. The study was done only on a few selected syndromes during a three-month period. It is possible that the study was conducted during an outbreak period and that the prevalence may be lower if patients were enrolled, round the year. IgM ELISA is the most appropriate among the currently available tests, for the diagnosis of acute M. pneumoniae infection. This test has a specificity of 98% in all stages of infection, but the sensitivity varies depending on the stage of infection(4). When compared to PCR, the test is less sensitive in very early infection(4,6) but is more sensitive in acute and convalescent phases of disease(4). Overall, IgM ELISA has a better sensitivity than PCR(4). One problem associated with use of IgM antibodies for dignosis, however, is that these antibodies remain for a few months after recovery. Since children in developing coun-tries like India can have several episodes of ARI per year, it is possible that some of the antibody positivity indicate recent past infec-tions. Even so, the prevalence of M. pneu-moniae infection is high in this area. Some reports from the west show the prevalence to be highest in the age group 5-20 years(1). However, in our stdy and in another study from Tamil Nadu(3), prevalence of infection was high in children below 5 years of age suggesting an earlier exposure. As is known(10), our data also shows that PAT lacked sensitivity. Cold agglutinins can be demonstrated in a variety of other infections like that due to adenovirus, RSV, influenza virus and in a variety of other tropical diseases(6). This was reflected in the low specificity of CA in our hands. Further studies are required to confirm these findings and to describe the spectrum of illnesses and seasonality of infection with this agent. Contributors: EM and TC designed the study and drafted the manuscript. EM will act as the guarantor of the study. SV and TC enrolled the patients. PK and IU performed the tests under supervision of EM. EM and PK analyzed the data. Funding:
Fluid Research Grant, Christian Medical College and Hospital, Vellore.
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