[show abstract][hide abstract] ABSTRACT: Prior to the introduction of Haemophilus influenzae type b (Hib) conjugate vaccines, invasive Hib disease affected almost exclusively children. According to some recent studies, in the postvaccine era, adults, the elderly, and immunocompromised persons can be affected more often than children. As the production of type-specific anti-capsular polysaccharide antibodies is the major defense mechanism against Hib, individuals with defects in humoral immune responses have high susceptibility to infections caused by Hib. We hypothesized that nonvaccinated adults with chronic conditions causing immunosuppression may lack protective antibody to Hib. We assessed serum anti-Hib IgG levels and bactericidal activity in 59 patients with chronic renal failure, 30 patients with type 2 diabetes mellitus, 28 patients with chronic obstructive pulmonary disease (COPD), and 20 patients with multiple myeloma compared to 32 healthy controls of similar age. Considering antibody at >0.15 μg/ml as the protective correlate in unvaccinated individuals, we detected subprotective Hib antibody levels in 29% of chronic renal failure, 20% of diabetes, 14% of COPD, and 55% of myeloma patients compared to 3% of healthy controls. Additionally, 70% of myeloma and 58% of chronic renal failure patients did not have detectable serum bactericidal activity against Hib. Among individuals with severe diseases causing secondary immunodeficiency, patients with multiple myeloma and chronic renal failure are at an increased risk of invasive Hib disease. Considering that Hib continues to circulate in the population, this study provides a rationale for the immunization of some adult patients with secondary immunodeficiency with the pediatric Hib vaccine to achieve protective immunity.
[show abstract][hide abstract] ABSTRACT: Prevalence of non-typeable Haemophilus influenzae (NTHi) in the etiology of invasive infections in immunocompromised individuals is increasing. Serum IgG antibody levels to H. influenzae protein D (PD) were significantly lower in adults suffering from chronic conditions causing secondary immunodeficiency (COPD, cancer, chronic renal failure, and diabetes) compared to age-matched healthy controls. A lack of naturally acquired antibody against this highly conserved antigen may contribute to an increased susceptibility to invasive NTHi disease. As COPD patients frequently infected with NTHi during disease exacerbations were unable to develop antibody response to PD, such defect could potentially contribute to the pathogenesis. Considering that pediatric PD-containing vaccines show protective effect against NTHi-caused otitis media, our data suggest the possibility of improving the defense against NTHi in COPD patients using immunization against PD. Although more research on the role of anti-PD antibody in protection against invasive NTHi disease is warranted, development of adult formulations of PD-based vaccines may be advantageous for prevention of severe infections in immunocompromised individuals.