Infectious diseases, also known as transmissible diseases or communicable diseases, comprise clinically evident illness (i.e., characteristic medical signs and/or symptoms of disease) resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism. In certain cases, infectious diseases may be asymptomatic for much or even all of their course in a given host. In the latter case, the disease may only be defined as a "disease" (which by definition means an illness) in hosts who secondarily become ill after contact with an asymptomatic carrier. An infection is not synonymous with an infectious disease, as some infections do not cause illness in a host.
Infectious pathogens include some viruses, bacteria, fungi, protozoa, multicellular parasites, and aberrant proteins known as prions. These pathogens are the cause of disease epidemics, in the sense that without the pathogen, no infectious epidemic occurs.
The common cold (also known as nasopharyngitis, rhinopharyngitis, acute coryza, head cold, or simply a cold) is a viral infectious disease of the upper respiratory tract which primarily affects the nose. Symptoms include coughing, sore throat, runny nose, sneezing, and fever which usually resolve in seven to ten days, with some symptoms lasting up to three weeks. Well over 200 viruses are implicated in the cause of the common cold; the rhinoviruses are the most common.
A cough medicine (or linctus, when in syrup form) is a medicinal drug used in an attempt to treat coughing and related conditions. For dry coughs, treatment with cough suppressants (antitussives) may be attempted to suppress the body's urge to cough. However, in productive coughs (coughs that produce phlegm), treatment is instead attempted with expectorants (typically guaifenesin, in most commercial medications) in an attempt to loosen mucus from the respiratory tract.
There is no good evidence for or against the use of these medications in those with a cough. Even though they are used by 10% of American children weekly, they are not recommended in children 6 years of age or younger because of lack of evidence showing effect and concerns of harm.
Acute bronchitis is an inflammation of the large bronchi (medium-size airways) in the lungs that is usually caused by viruses or bacteria and may last several days or weeks. Characteristic symptoms include cough, sputum (phlegm) production, and shortness of breath and wheezing related to the obstruction of the inflamed airways. Diagnosis is by clinical examination and sometimes microbiological examination of the phlegm. Treatment for acute bronchitis is typically symptomatic. As viruses cause most cases of acute bronchitis, antibiotics should not be used unless microscopic examination of gram-stained sputum reveals large numbers of bacteria.