Communicable diseases are everywhere--on your hands, the doorknobs, the faucets, your friends' faces and in your children's noses. Communicable diseases are illnesses that can be passed from person to person, either by direct contact or indirectly, by touching something someone else left their germs on. "Germs" is a generic way to refer to viruses, bacteria and fungi; all communicable diseases are caused by some type of germ; some are airborne, others are transmitted on the hands or other objects.
Common Cold
The term "common cold" is a misnomer; there are actually more than 200 airborne viruses that can cause a cold, the Mayo Clinic states, although the most common culprit is the extremely contagious rhinovirus. Adults may have two to four colds a year, while children may be sneezing, sniffling and coughing four to six times a year. Cold symptoms are usually mild; people with colds don't usually run a fever. Cold viruses can lead to complications such as ear infection, bronchitis, pneumonia or upper airway disease such as croup or asthma. Antibiotics are useless against viruses that cause colds, but may help if bacterial infections complicate a cold.
Influenza
Influenza, another common, very contagious airborne virus, is sometimes thought of as the "big brother" of a cold, but colds and influenza are totally different entities. Influenza viruses are classified as A, B or C by the proteins they're made up of, with A being the most common cause of influenza, or flu. Influenza A viruses appear every two to three years, compared to type B viruses, which cycle through every three to five years, on average, and cause milder disease, the Merck Manual states. Type C doesn't cause typical influenza.
Flu symptoms are more severe than those caused by colds, although the initial symptoms of runny nose and sore throat are similar; fever is common, lethargy or a sense of profound exhaustion with chills and severe muscle aches are common. Headache may be severe; cough is more pronounced in flu as well. Flu lasts up to a week, but fatigue may last several weeks after the infection. Bacterial complications such as pneumonia are more common after the flu, especially in the elderly and very young children.
Gastroenteritis
Many people refer to gastrointestinal infections as the flu, although the viruses responsible are not influenza germs and are not airborne viruses; they're transmitted by poor hand washing to surfaces or food by people who carry the germs in their intestines. Gastrointestinal infections can be bacterial, as in the case of salmonella, but are more commonly viral, such as the rotavirus or norovirus, which often cause large outbreaks in confined areas such as cruise ships. Gastroenteritis causes vomiting, diarrhea, headache, fever and abdominal cramps. The elderly and very young can become dehydrated and may need hospital care to replace fluids.
