Estimated and reported incidence of pertussis in Estonian adults: A seroepidemiological study.
OBJECTIVE
Rates of pertussis immunisation among children in Estonia are high (∼95%), but pertussis is still the most common vaccine preventable childhood disease. Adults are suspected to be sources of pertussis in children. We aimed to measure pertussis toxin (PT) IgG in adults to estimate pertussis infection activity and compare estimated and reported pertussis incidences.


METHODS
In a cross-sectional serosurvey, consecutive leftover blood sera (n=3327) from subjects aged 20-99 years old were collected at Quattromed HTI laboratories between the 7th January and 27th February 2013. Anti-PT IgG concentration was measured by ELISA (Euroimmun, Lübeck, Germany). Estimated annual pertussis incidence was calculated for 10-year age classes using de Melker et al. (2006. J Infect. 53(2):106-13) formula.


RESULTS
The mean number of samples in each 10-year age class was 466 (SD 20.5), except for 90-99 year olds which contained 65 samples. More than half of all subjects (58.1%) had anti-PT IgG <5.0IU/mL, 2.7% had 62.5 to <125IU/mL and 0.6% ≥125IU/mL; no differences occurred between 10-year age classes. Estimated incidence of pertussis infection was 5.8% (95% CI 4.8-7.0) in 2012, with peaks observed in 20-29 year olds (11.0%; 95% CI 7.4-15.6) and 90-99 year olds (10.8%; 95% CI 3.0-26.2). Estimated pertussis incidence rate was 915 times higher than reported. Of 80 subjects with anti-PT IgG ≥62.5IU/mL, 25 (31.3%) had complained of coughing to their GP during the previous six months.


CONCLUSIONS
The frequency of pertussis infection was similar for all ages, suggesting similar Bordetella pertussis activity in adults and children. The wide gap between reported and estimated incidence indicates poor recognition of pertussis, likely owing to it being an asymptomatic or mild disease.
Institute of Microbiology, University of Tartu, Ravila 19, Tartu 50411, Estonia; Children's Clinic of Tartu University Hospital, Lunini 6, Tartu 51014, Estonia. Electronic address: Piia.Jogi@kliinikum.ee.
Piia
P
Jõgi
Department of Family Medicine, University of Tartu, Puusepa 1a, Tartu 50406, Estonia.
Marje
M
Oona
Department of Public Health, University of Tartu, Ravila 19, Tartu 50411, Estonia.
Karolin
K
Toompere
Institute of Microbiology, University of Tartu, Ravila 19, Tartu 50411, Estonia.
Irja
I
Lutsar
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000907:Antibodies, Bacterial / Q000097:blood*; D001886:Bordetella pertussis / Q000276:immunology*; D003430:Cross-Sectional Studies; D004797:Enzyme-Linked Immunosorbent Assay; D004957:Estonia / Q000453:epidemiology; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D015994:Incidence; D008297:Male; D008875:Middle Aged; D016036:Seroepidemiologic Studies; D014917:Whooping Cough / Q000453:epidemiology*; D055815:Young Adult
D000907:Antibodies, Bacterial; D007074:Immunoglobulin G
Anti-PT IgG; Immunisation; Pertussis incidence; Seroepidemiology; Whooping cough