Microbiological Characterization of Haemophilus influenzae Isolated from Patients with Lower Respiratory Tract Infections in a Tertiary Care Hospital, South India.

INTRODUCTION: Haemophilus influenzae is responsible for wide range of localized and invasive lower respiratory tract infections (LRTI) with the highest burden of disease in low and middle income countries.

AIM: The aim of the present study was to characterize the H.influenzae isolates from suspected LRTI.

MATERIALS AND METHODS: A prospective study was conducted over a period of one and half years (December 2012 to May 2014) including patients with LRTI. H.influenzae was isolated from lower respiratory specimens following standard procedures. Complete characterization of the isolates was performed by bio typing, capsular serotyping, molecular genotyping and antibiotic susceptibility testing. The predisposing factors and clinical presentation were studied in the infected patients.

RESULTS: A total of 8995 samples were received during the study period, out of which growth was significantly observed in 2848 (31.7%) samples. Among the various respiratory pathogens, H.influenzae was isolated from 175 (6.14%) patients. Majority (78.9%) of the patients presented with acute exacerbations of chronic obstructive pulmonary disease. The isolates most frequently were of Biotype II (35.42%). Only four of the 50 isolates subjected to capsular serotyping were typeable and were of type b, e and f. All the 50 isolates tested were found to be non-typeable by PCR for capsular genotyping. Maximum resistance was found against ampicillin (9.71%).

CONCLUSION: H.influenzae was found to be a significant cause of LRTI. Majority of the isolates were found to be non typeable strains. Non typeable H. influenzae isolates should not be neglected as they can colonize the respiratory tract in COPD patients and can lead to biofilm formation and treatment failure.