Infection is the invasion of an organism’s body tissues by disease-causing agents, their multiplication, and the reaction of host tissues to these organisms and the toxins they produce. Infections are caused by infectious agents such as viruses, viroids, prions, bacteria, and parasites.

The microorganism infecting the human can either be a primary pathogen or an opportunistic pathogen. A Primary pathogen causes disease as a result of their presence in a healthy individual. Opportunistic pathogen causes infection in a immunocompromised individual.

Infection can also be classified according to the location, including:

  • Urinary tract infection
  • Skin infection
  • Respiratory tract infection
  • Tooth infection
  • Vaginal infection
  • Intra-amniotic infection

The symptoms of infection depend on the organism that caused it. Each organism also has its own treatment method.

  • Bacteria. Most bacteria are harmless, and some actually help by digesting food, destroying disease-causing microbes, fighting cancer cells, and providing essential nutrients. Fewer than 1% of bacteria cause diseases in people.
  • Viruses. Unlike bacteria, viruses can’t survive without a host. They can only reproduce by attaching themselves to cells. Also unlike bacteria, most viruses do cause disease, and they’re quite specific about the cells they attack.

Bacterial and viral infections can cause similar symptoms such as coughing and sneezing, fever, inflammation, vomiting, diarrhea, fatigue, and cramping — all of which are ways the immune system tries to rid the body of infectious organisms.


You should consult your doctor if you think you have a bacterial or viral infection. Exceptions include the common cold, which is usually not life-threatening.

In some cases, it’s difficult to determine the origin of an infection because many ailments — including pneumonia, meningitis, and diarrhea — can be caused by either bacteria or viruses.

If necessary, he or she also can order a blood or urine test to help confirm a diagnosis, or a “culture test” of tissue to identify bacteria or viruses. Occasionally, a biopsy of affected tissue may be required.



Bacterial infection are treated with anti-bacterials or antibiotics. The discovery of antibiotics for bacterial infections is considered one of the most important breakthroughs in medical history. Unfortunately, bacteria are very adaptable, and the overuse of antibiotics has made many of them resistant to antibiotics. This has created serious problems, especially in hospital settings.

Viral infections are treated with anti-virals, but vaccines are also used to prevent infection. Vaccines have drastically reduced the number of new cases of viral diseases such as polio, measles, and chickenpox. In addition, vaccines can prevent such infections such as the flu, hepatitis A, hepatitis B, human papillomavirus (HPV), and others. But the treatment of viral infections has proved more challenging, primarily because viruses are relatively tiny and reproduce inside cells.

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