Survival Rate of Haemophilus Influenzae Isolated from Pediatric Patients in Commercial Transport Systems

Background: Haemophilus influenzae (HI) remains a leading cause of meningitis among unvaccinated children. Studies revealed that HI accounted for 7% of identified etiologic agents of childhood community-acquired pneumonia in North America and Europe and 21% in Africa and South America. Fastidious organisms such as HI may survive only a few hours after specimen collection if placed in swab transport systems and this can be a critical component in the success of the diagnostic process. The purpose of this study was to evaluate multiple lot numbers of Amies Gel swabs from two manufacturers namely Copan, Ca, USA (M40 Transystem, 3 lots) and Starplex Scientific, Ont, Canada (Starswab II, BactiSwab and Fisherfinest, 1 lot of each) for the survival of HI over a 48hr period at room temperature (RT).
Methods: Five HI clinical isolates from pediatric patients and one HI ATCC 10211 were tested at RT (25°C) against 3 lot numbers from both manufacturers using the Swab Elution Method described in NCCLS M40-A. A 0.5 McFarland suspension of each sample was performed in 0.85% physiological saline from a 24hr growth of the organism. Ten-fold dilutions were prepared and the swabs were inoculated in triplicate with 100μl of each sample suspension. Swabs were held at RT for 0, 6, 24 and 48hr. Duplicate plate counts were performed at 35°C after each holding time point to determine organism survival rate.
Results: Cultures from all swab dilutions were averaged. Bacterial recovery from swabs held for 0 and 6 hr were similar for all swab lot numbers from both manufacturers. After 24hr incubation, bacterial viability from Starplex lots was dramatically lower compared to that from Copan. At the 48hr time point all three Starplex swab lots demonstrated a significant loss in viability with two of six HI strains and four HI strains failed to survive. Only Copan swabs were able to maintained viability of all six HI strains tested after 48hr at RT.
Conclusion: Survival of HI varies between manufacturers Amies products and does not appear to be lot number dependent. Only Copan swab lots were able to comply with criteria for HI organism survival at all time points as described in NCCLS M40-A document.