Multiple epidemics per year and more prolonged virus circulation might also limit the pool of susceptible children.
Although several empirical studies have linked school activities with influenza virus transmission (2 – 10 ), few studies have considered data from multiple epidemic periods, and little information is available from the Southern Hemisphere.
68 Furthermore, dengue and yellow fever caused multiple epidemics in the southern parts of the USA in the 18th, 19th, and early 20th centuries.
Thus, using data from short time intervals can be complementary to using groups composed of related individuals and data from multiple epidemics.
Despite this, multiple epidemics of infection with the same virus subsequently occurred in Singapore and elsewhere in late 2009 and 2010 [ 4, 5], with some evidence of shifts in age distribution to involve older individuals [ 6, 7].
Longer-term data sets at the high-resolution of individuals but spanning multiple epidemics are becoming available, with the current interest in transmission networks and the interface of Geographic Information Systems and disease patterns.
As Dr. Helene D. Gayle, who directs AIDS programs at the disease control centers in Atlanta, says, "It is multiple epidemics".
Likewise, multiple epidemics of sleeping sickness have occurred in Africa, particularly in Uganda, where both Trypanosoma subspecies are endemic.
After multiple epidemics among freed people, smallpox assumed a negative association with blackness, further adding to the popular belief that sufferers were both filthy and inferior.
Mr. Draper said the diseased seedlings, found in stores as far west as Ohio, were at least one source of the illness, but, he added, "It's possible that we are looking at multiple epidemics".
