Rapid diagnosis of H. influenzae Type b infections possible with PCR

By C. Vidyashankar, MD

DELHI (Reuters Health) – Polymerase chain reaction can be used for the early diagnosis of infections caused by Haemophilus influenzae Type b (Hib), a leading cause of pneumonia and meningitis in children under 5 years of age, researchers from Bangladesh report.

As reported in the December 2001 issue of Journal of Health Population and Nutrition, Dr. Shereen Shoma and colleagues from the International Center for Diarrheal Diseases Research and the University of Dhaka, compared the effectiveness of PCR with that of culture in detecting invasive Hib infection in samples taken from 320 children less than 5 years of age who presented with acute febrile illness.

Of these, 180 children were clinically diagnosed with pneumonia, 120 with meningitis and the rest with non-specific febrile illness. Blood culture and antibiotic sensitivity for Hib were carried out in patients with pneumonia and non-specific febrile illness, while cerebrospinal fluid culture was done in children suspected as having meningitis. DNA extracted from serum and cerebrospinal samples was analyzed for presence of Hib using PCR based on the bexA gene as primer.

The researchers observed that blood cultures were positive for Hib in 16 of 180 children with pneumonia, while PCR was positive in 21 children. In cerebrospinal fluid, Hib was grown in 15 of the 120 culture samples and Hib DNA was detected using PCR in 23 samples.

Serum PCR had a sensitivity, specificity and accuracy of 93.7%, 96.7% and 96.5% respectively in detecting pneumonia due to Hib, Dr. Shoma and colleagues note. In the diagnosis of meningitis, polymerase chain reaction had a sensitivity of 100% and a specificity of 92.4%, they add.

While noting that their results were in agreement with previous studies, the researchers point out that their use of serum as a source and of agarose gel electrophoresis rather than hybridization in the polymerase chain reaction process could be responsible for the slightly lower sensitivity seen in children with pneumonia.

Over 80% of the Hib isolates were resistant to co-trimoxazole, and nearly half were resistant to co-trimoxazole, ampicillin and chloramphenicol. The high levels of multi-drug resistance "is a matter of great concern," the researchers caution.

It is possible to establish a diagnosis of Hib infection and the antibiotic sensitivity patterns within half an hour using polymerase chain reaction, the Bangladesh team notes. This "gives the hope of improved management of meningitis and pneumonia in children."

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