Viruses Coronaviruses are a group of viruses known for causing the<unk> . They have a halo or crown-like (corona) appearance when viewed under an electron microscope. The<unk>  is an infection of the upper respiratory tract which can be caused by many different viruses. The most<unk> ly implicated is a rhinovirus (30–80%), a type of picornavirus with 99 known serotypes. Other<unk> ly implicated viruses include human coronaviruses (≈ 15%), influenza viruses (10–15%), adenoviruses (5%), human respiratory syncytial virus (RSV), enteroviruses other than rhinoviruses, human parainfluenza viruses, and human metapneumovirus. Frequently more than one virus is present. In total, more than 200 viral types are associated with<unk> s. Transmission The<unk>  virus is typically transmitted via airborne droplets (aerosols), direct contact with infected nasal secretions, or fomites (contaminated objects). Which of these routes is of primary importance has not been determined. The viruses may survive for prolonged periods in the environment (over 18 hours for rhinoviruses) and can be picked up by people's hands and subsequently carried to their eyes or nose where infection occurs. Transmission from animals is considered highly unlikely; an outbreak documented at a British scientific base on Adelaide Island after seventeen weeks of isolation was thought to have been caused by transmission from a contaminated object or an asymptomatic human carrier, rather than from the husky dogs which were also present at the base. Transmission is<unk>  in daycare and at school due to the proximity of many children with little immunity and frequently poor hygiene. These infections are then brought home to other members of the family. There is no evidence that recirculated air during commercial flight is a method of transmission. People sitting in close proximity appear to be at greater risk of infection. Rhinovirus-caused<unk> s are most infectious during the first three days of symptoms; they are much less infectious afterwards. Weather A<unk>  misconception is that one can "catch a<unk> " simply through prolonged exposure to<unk>  weather. Although it is now known that<unk> s are viral infections, the prevalence of many such viruses are indeed seasonal, occurring more frequently during<unk>  weather. The reason for the seasonality has not been conclusively determined. Possible explanations may include<unk>  temperature-induced changes in the respiratory system, decreased immune response, and low humidity causing an increase in viral transmission rates, perhaps due to dry air allowing small viral droplets to disperse farther and stay in the air longer. The apparent seasonality may also be due to social factors, such as people spending more time indoors, near infected people, and specifically children at school. Although normal exposure to<unk>  does not increase one's risk of infection, severe exposure leading to significant reduction of body temperature (hypothermia) may put one at a greater risk for the<unk> ; although controversial, the majority of evidence suggests that it may increase susceptibility to infection. Other Herd immunity, generated from previous exposure to<unk>  viruses, plays an important role in limiting viral spread, as seen with younger populations that have greater rates of respiratory infections. Poor immune function is a risk factor for disease. Insufficient sleep and malnutrition have been associated with a greater risk of developing infection following rhinovirus exposure; this is believed to be due to their effects on immune function. Breast feeding decreases the risk of acute otitis media and lower respiratory tract infections among other diseases, and it is recommended that breast feeding be continued when an infant has a<unk> . In the developed world breast feeding may not be protective against the<unk>  in and of itself.
Common cold
Whooping cough
Pontiac fever
Allergic rhinitis
Polymer fume fever
Sinusitis
Plague 
Bronchitis