URTI (Upper Respiratory Tract Infections) and LRTI (Lower Tract Respiratory Infections) are mostly caused by viruses; sometimes they can be caused by bacteria.
In the URTI class we find laryngitis, tracheitis and bronchitis. The main symptom is cough; other symptoms are fever, headache and pains. If the infections occurs in the nose, there could be also cold symptoms. Upper respiratory infections are one of the most frequent causes of doctors visits with varying symptoms ranging from runny nose, sore throat and cough, to breathing difficulty and lethargy. In the United States, upper respiratory infections are the most common illness leading to missing school or work.
The peak of these symptoms is usually 2 or 3 days after the infection. The cough may persist even if the infection has disappeared. The reason is that the inflammation in the airways, caused by the infection, is a little bit longer to settle. Sometimes it takes 3 weeks to clear it completely.
Most URTI do not cause complications. A URTI may trigger coughing, wheezing and shortness of breath if the patient suffers of asthma or other lung diseases. Sometimes the infection can travel to the lung tissue, sinuses or ears. It is very difficult to prevent URTI since they are caused by a lot of different viruses (mostly adenovirus and rhinovirus), and it is easier to have an URTI living or working in crowded places such as public transportations and schools.
Although upper respiratory infections can happen at any time, they are most common in fall and winter months, from September to March. It may be due to the fact that these are the usual school months when children spend a lot of time in groups and inside closed doors. Furthermore, many viruses of upper respiratory infections thrive in the low humidity of winter.