It's often difficult to determine that an illness is a direct result of pesticide poisoning, yet many studies link a wide variety of health problems to such exposure.

CNN: Children face danger in the schoolyard grass from pesticides

In addition, it's easy to confuse seasonal flu for an illness caused by a number of other pathogens, including rhinovirus.

CNN: Flu shot myths addressed

Some only have a short-term illness, while around a third continue to have symptoms into adulthood - but it is hard to predict how an individual's illness will progress.

BBC: Health