Invasive disease caused by Haemophilus influenzae in Sweden 1997–2009; evidence of increasing incidence and clinical burden of non‐type b strains

Introduction of a conjugated vaccine against encapsulated Haemophilus influenzae type b (Hib) has led to a dramatic reduction of invasive Hib disease. However, an increasing incidence of invasive disease by H. influenzae non‐type b has recently been reported. Non‐type b strains have been suggested to be opportunists in an invasive context, but information on clinical consequences and related medical conditions is scarce. In this retrospective study, all H. influenzae isolates ( n = 410) from blood and cerebrospinal fluid in three metropolitan Swedish regions between 1997 and 2009 from a population of approximately 3 million individuals were identified. All available isolates were serotyped by PCR ( n = 250). We observed a statistically significant increase in the incidence of invasive H. influenzae disease, ascribed to non‐typeable H. influenzae (NTHi) and encapsulated strains type f (Hif) in mainly individuals >60 years of age. The medical reports from a subset of 136 cases of invasive Haemophilus disease revealed that 48% of invasive NTHi cases and 59% of invasive Hif cases, respectively, met the criteria of severe sepsis or septic shock according to the ACCP/SCCM classification of sepsis grading. One‐fifth of invasive NTHi cases and more than one‐third of invasive Hif cases were admitted to intensive care units. Only 37% of patients with invasive non‐type b disease had evidence of immunocompromise, of which conditions related to impaired humoral immunity was the most common. The clinical burden of invasive non‐type b H. influenzae disease, measured as days of hospitalization/100 000 individuals at risk and year, increased significantly throughout the study period.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87052/1/j.1469-0691.2010.03417.x.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/87052/2/CLM_3417_sm_FigS1.pd