Abstract:

Our aim was to document the prevalence of chlamydial infection in children less than five years of age with Community Acquired Pneumonia (CAP). Seventy-three children, 1 month to 5 years of age, hospitalized with CAP were enrolled over a period of one year. Microimmunofluorescence (MIF) was done to detect IgM antibodies against Chlamydia sp. in sera of all patients; PCR was performed to detect C. pneumoniae DNA in nasopharyngeal aspirates. The prevalence of Chlamydia species infection in CAP in children < 5 years of age was 5.5% (4/73). Two cases were positive for C. trachomatis antibodies; one case was positive for C. pneumoniae antibodies and one case was positive for C. pneumoniae DNA. Chlamydia sp. have an important role in CAP in children <5 years and for early diagnosis of infection, use of more than one method i.e. PCR and serology both is advisable.

Key words: Chlamydia species, community-acquired pneumonia, MIF, PCR

C. pneumoniae ranks among the three most common etiologic agents of community acquired pneumonia (CAP)(1). A specific diagnosis is important, because β-lactam antibiotic treatment is ineffective in infections due to Chlamydia(2). The organism may be causally associated with wheezing, asthmatic bronchitis and adult onset asthma(3). Prevalence of C. pneumoniae in children <5 years of age varies from 0 to 11%(4,5). Presence of nasopharyngeal C. trachomatis is also associated with a pneumonitis syndrome of infancy(6). MIF test is considered the gold standard for estimation of Chlamydia species specific antibodies(7). PCR on nasopharyngeal specimen is a rapid and sensitive method for detection of C. pneumoniae(8). The present study was conducted to detect the prevalence of Chlamydial infection in children less than five years of age hospitalized with community-acquired pneumonia.

Subjects between one month to 5 years, hospitalized with severe to very severe pneumonia, from August 2004 to August 005 were enrolled. Children with comorbid conditions, immuno-compromised status and congenital heart disease were excluded. All blood samples were tested for IgM antibodies against Chlamydia pneumoniae, C. trachomatis and C. psittaci using MIF (Chlamydia IgM sero FIA kit, Savyon Diagnostics Ltd., Israel). Presence of IgM antibodies in titer >1:16 was labeled as acute infection(9). Nasopharyngeal aspirates were obtained by passing an infant feeding tube through each nostril; secretions were aspirated for PCR by syringe suction. A pair of Chlamydia pneumoniae specific oligonucleotide primers Cpn A and Cpn B based on 16S rRNA gene (Bangalore genei Pvt. Ltd., India) were used for amplification(10).

We enrolled 73 cases (mean age 12.7 mo). Of these, 53 were male and 20 were females. Forty-three had rural background and 30 were from urban area. On MIF, three of the 73 (4.1%) patients were positive for IgM antibodies in titer >1:16 against Chlamydia species. Of these one was positive for C. pneumoniae while 2 were positive for C. trachomatis. One patient was positive for C. pneumoniae by PCR; however, it was not the same patient who had IgM antibodies against C. pneumoniae. Thus, overall 4/73 (5.5%) patients tested positive for Chlamydia species. C. psittaci was not detected in any sera.

In present study, infection with Chlamydia pneumoniae and C. trachomatis both were found to be low despite using two methods i.e. MIF and PCR. This is in contrast to previous studies, which reported a prevalence of 6.4 and 11% based on ELISA results alone(4,11). They included children of all ages and ELISA is known to be less specific than MIF. Specific antibodies to C. pneumoniae are uncommon in children under age of 5 years using MIF(12). Hence, use of 2 methods i.e., MIF and PCR is advised.

IgM response appears 3 weeks after onset of C. pneumoniae infection, and may be absent in reinfection(13). In one of our PCR positive and IgM negative C. pneumoniae patient, total duration of illness was 8 days, in contrast to IgM positive patient, in whom duration of illness was 21 days. Moreover, culture documented, acute infection without sero conversion is known(14). These patients however can be considered simple carriers as asymptomatic nasopharyngeal carriage has been reported in adults and children(15). PCR negative and IgM positive C. pneumoniae infection could be due to clearance of organism from the respiratory tract while antibodies start appearing.

C. trachomatis pneumonia is usually apparent in infants between 4 to 2 weeks of age(16). While in our study, cases were 9 to 26 months old respectively. In present study authors did not find any particular clinical correlation with the laboratory diagnosis of chlamydial infection. But the number of positive patients is too low to draw any conclusions. Further studies with large number of patients are required to find out role and clinical characteristics of C. trachomatis and C. pneumoniae in CAP in children.

Contributors: RJ did the bench work, manuscript preparation and data processing. AJ was involved in planning of study, manuscript preparation and data processing. JA assisted in manuscript preparation and data processing. SA was the clinical collaborator.

Funding: None.

Competing interests: None.