In China, this disease previously occurred in a cyclical pattern at intervals of 8 10 years [ 1].
Many researchers have suggested that epizootics are cyclical events recurring at fairly regular intervals; the length of interepidemic intervals has been interpreted as the time required for reconstitution of susceptible monkey populations (6, 7 ).
Between the periods, three major DENV-1 outbreaks occurred in 1987 , 1997and 2004 with a cyclical pattern of ~8 years interval [ 8, 33].
These urban or predominantly peri-urban outbreaks appear to be increasing, but historically they are cyclical and recur following several year intervals of low endemicity.
In addition, cyclical epidemics occur at 3 9 year intervals, but high rates of transmission usually continue during the inter-epidemic periods.
Legend OR, Odds ratio; CI, Confidence interval x adjusted for cyclical and secular trends *likelihood ratio test for interaction in stage III, phase in stages I and II.
Legend: RR, Risk ratio; CI, Confidence interval x adjusted for cyclical and secular trends, *Wald test for socio-demographic variable, ~ likelihood ratio test for interaction in stage III, phase in stages I and II.
The risk estimates following the use of the continuous combined oestrogen progestin regimens were generally higher than following the cyclical combined regimens, but with overlap in confidence intervals.
However, in 3%5%% of the women cyclical attacks are severe and frequent (up to 2 4 weeks interval), 17, 47 which disable their lives.
To perform such analysis would have required collection of pre- and post-intervention data at equally spaced time intervals that span enough periods to detect pre-existing trends and cyclical patterns.
