Antibodies prevalence against Haemophilus influenzae type b in Jeddah population, Saudi Arabia. I. Total antibodies.

In this national comprehensive seroprevalence study, indirect ELISA test was used to evaluate Haemophilus influenzae type b (Hib) anti-polyribosyl-ribitol phosphate (PRP) total antibodies (IgM, IgG, IgA) in 1,003 sera samples from routine medical check-up of healthy individuals attending the local medical facility in Jeddah, Saudi Arabia in the period from February 2014 to January 2016. Serum anti-CPS antibodies confer immunity against invasive Hib disease. An anti-CPS concentration of ⩾ 0.15 μg/mL is believed to be a serological indication for short-term immunity protection against invasive Hib disease, while a concentration of ⩾ 1.0 μg/mL is believed to be long-term protective. Results showed higher level of anti-Hib IgG (2.41 μg/ml average geometric mean concentration (GMC) regardless of age and gender, followed by levels of IgM (0.91 μg/ml) and IgA (0.34 μg/ml), reflecting the community immunity against Hib. Low anti-Hib level (< 0.15 μg/ml of anti-PRP IgG) in elderly people (males aged 57-91 years and females aged 35-64 years) may indicate a need for a booster dose of Hib vaccine to elderly people in the community. The IgG prevalence over IgM, and IgM prevalence over IgA indicate the major role of IgG over IgM and IgA in keeping immunity in the track against Hib. Low level of IgM and IgA comparing to IgG may indicate the absence of Hib acute infections in the population.