In some ways, the infections caused by bacteria and viruses are alike. They can each cause similar symptoms such as fever, coughing, vomiting, diarrhea, fatigue, and cramping. They are both capable of causing short-lived acute infections as well as chronic infections, that untreated, can last a lifetime. Also, viruses and bacteria lend themselves to preventive measures, such as the use of vaccines.
Bacterial infections occur when harmful bacteria enter the body. Often this happens because the organism takes advantage of a situation, such as a break in the 
skin or a compromised immune system. This is called an “opportunistic” infection. Some of the most common types of bacterial infections are caused by:
- Staph (Staphylococci) are bacteria that are commonly found on the skin or in the nose of healthy individuals. Some types of Staph bacteria can cause serious infections of the skin, heart, lungs, or blood stream. A particularly serious type of Staph infection is called MRSA (methicillin-resistant Staphylococcus aureus). MRSA does not respond to the typical antibiotics used to treat Staph infections.
- Strep (Streptococci) infections include “strep throat”; a common skin infection in children called impetigo; toxic shock syndrome; and a form of pneumonia.
- H. flu (Haemophilus influenza), despite its name, does not cause the flu. At one time, it was mistakenly considered to be the cause of influenza until it became apparent that the flu was caused by a virus. It is one of the most common causes of middle ear infections (otitis media) in children.
- E. coli (Escherichia coli) bacteria commonly live in the gastrointestinal tract of humans and even serve useful purposes, such as producing Vitamin K. A disease-producing strain of E. coli can cause food poisoning if transmitted through improperly cooked hamburger, or other food products.
- There are many other infections caused by bacteria including tuberculosis, pelvic inflammatory disease, Lyme disease, tetanus, and bacterial pneumonia.
An antibiotic is usually needed to treat bacterial infections. Antibiotics either kill bacteria, or interrupt their ability to multiply. This gives the body’s defenses an opportunity to take over and fight the infection. The names of antibiotics that are effective against different strains of bacteria include the penicillins (e.g. ampicillin), cephalosporins (e.g. Keflex), tetracyclines (e.g. Vibramycin), quinolones (e.g. Cipro) and macrolides (erythromycin).
Vaccines may also be available to prevent bacterial infections. Effective vaccines have been developed for a number of bacterial infections including diphtheria, tetanus, whooping cough, meningococcal meningitis, pneumococcal pneumonia, and typhoid fever.
Viral infections include the common cold, influenza, measles, AIDS, hepatitis A & B, rabies, 
chicken pox and shingles. In contrast to bacteria, viruses must invade a living cell to reproduce. Once inside the host cell, the virus’s genetic material (DNA or RNA) takes control of the cell and forces it to replicate the virus. The infected cell eventually dies, releasing the new viruses which go on to infect other cells. Viral infections are generally more difficult to treat than bacterial infections because the virus “hides” inside normal, living cells protecting them from treatment with antibiotics.
Because of the overlap in symptoms, it can be difficult for someone to know if a condition, such as diarrhea is being caused by a bacteria or virus. When the diagnosis is uncertain, doctors can usually tell which is responsible with a careful history and physical examination. Sometimes, special testing, such as a “culture test” to grow the specific organism, may also be used.
Many viral infections, such as the common cold, do not presently have a treatment that is directed against the virus. In particular, the antibiotics used for treating bacterial infections, are ineffective against viruses. Fortunately, many viral infections are “self-limited” and the body’s immune system is able to fight off the infection. A few anti-viral drugs are available such as the ones used in treating a human immunodeficiency virus (HIV) infection, seasonal influenza, and cold sores. Another type of antiviral drug, called interferon, enhances the body’s immune response to the viral infection.
Most viruses attack specific areas of the body, such as the liver, genitals, or respiratory tract. In some instances the infected cell loses control of its normal function and develops into cancer. Examples of this include cervical cancer following an infection with the human papilloma virus (HPV) and liver cancer developing from a chronic hepatitis B infection.
Over the past century, immunizations have become an effective way to prevent viral infections. In fact, the first vaccine that was developed was used to prevent the viral illness, smallpox. Other viral diseases with effective vaccines include polio, measles, chickenpox, influenza, hepatitis A & B, and human papillomavirus (HPV) infections.