Background. We reported high levodopa use and prevalences of Parkinson
's Disease (PD) in periodically, time-clustered, Icelandic cohorts bor
n after major whooping cough epidemics (MWCE). Methods. In order to qu
antify a possible relationship between age at first post-birth MWCE an
d risk of PD we: 1) calculated cumulative incidences of PD during the
period 1954-1963 in one-year Icelandic cohorts born between 1869 and 1
927, using raw material from a reported survey; 2) identified MWCE fro
m 1869 onwards in Iceland; 3) estimated cohort ages at onset of incide
nce period and at first MWCE; and 4) combined the above-mentioned info
rmation using log-linear models. In addition, we studied the prevalenc
e of levodopa users in Icelandic birth cohorts during a recent period.
Results. The curves of the above-mentioned incidences and prevalences
in one-year birth-cohorts showed: 1) a similar, age-related, inverted
V profile; and 2) a systematic notchy pattern, with peak values for o
ne or both measurements for cohorts born during or after each of nine
MWCE identified during the period 1869-1927. When 13 cohorts born in y
ears with MWCE were excluded from the analysis, the risk of PD rose wi
th age at first defined MWCE, with the linear increase being 8.4% per
year (95% CI:-0.1-18.3%). Conclusions. These results are consistent wi
th reported effects of age at exposure in animal models of toxic parki
nsonism, age-related changes in the dopamine receptor-GPT-binding prot
ein-adenylatecyclase system observed in rats treated with pertussis to
xin, and some PD epidemiological features. They suggest that pertussis
neurotoxicity could be causally related to PD worldwide.