The infectious diseases of the respiratory tract that are associated with the rainy season are usually transmitted by droplets or by direct contact with objects that have been contaminated with the secretion of infected people.
The common cold is a generally benign and self-limiting infection of the nose and upper respiratory tract that is caused by many different viruses. The flu on the other hand, has more severe signs and symptoms than the common cold. It is also a viral infection, but the viruses that cause it are the influenza type A & B viruses, which frequently mutate and add new pathogenic strains to the influenza viral pool. The newest addition to the influenza viral pool is of course the much celebrated influenza A (H1N1) virus. The other upper respiratory tract infections that occur during the rainy season are likewise generally benign, but as in the case of flu and even the common cold, they sometimes complicate - pneumonia and bronchitis and become life-threatening.