Infectious Disease

Infectious diseases can be caused by bacteria, viruses, fungi or parasites.

Even when you try your best to avoid them with safe practices, infectious disease are sometimes unavoidable. They can be caused by:

  • Bacteria – The source of illnesses such as strep throat, pneumonia, urinary tract infections and tuberculosis.
  • Viruses – Responsible for many conditions including common colds, influenza, hepatitis B and C, varicella-zoster virus (which causes chicken pox and shingles) and HIV (the virus that causes AIDS).
  • Fungi­ – The origin of aspergillosis (a lung and sinus infection), coccidioidomycosis (an infection of the upper respiratory tract and lungs from airborne spores, also called valley fever), histoplasmosis (a lung infection traced to fungi in bird and bat droppings) and cryptococcosis (a pneumonia-like illness from airborne fungi that typically infects people with weakened immune systems).
  • Parasites – Transmitted by mosquito bites (malaria) or animal feces.

Infectious disease can be spread through:

  • Direct contact. You can become infected through direct contact with a person or animal that has the infection.
  • Indirect contact. Many disease-causing organisms (germs) can linger on a tabletop or faucet handle. You may become infected if you touch surfaces with germs, and then touch your eyes, mouth or nose.
  • Insects. Mosquitoes, fleas, lice or ticks can be disease carriers. Mosquitoes can carry the malaria parasite or the West Nile virus.
  • Contaminated food and water.  E. coli, for example, is a bacterium found in undercooked meat and unpasteurized fruit juice.


You can fight infectious diseases with proper hygiene and by taking some simple precautions. With the numerous vaccines and advanced medical technology available today, people are well equipped to avoid getting sick with many diseases like measles and chickenpox. To protect yourself and your family:

  • Wash your hands frequently. It’s particularly important to wash your hands before preparing food or eating, and after using the bathroom.
  • Get vaccinated. Immunizations drastically reduce your chance of disease.
  • Stay home if you’re sick. If you’re vomiting, have diarrhea or are running a fever, don’t go to work or school.
  • Prepare food safely. Keep kitchen surfaces clean, cook foods to the proper temperature and promptly refrigerate leftovers.
  • Practice safe sex. Use condoms if there’s a chance of sexually transmitted infections. Talk to your doctor about pre-exposure prophylaxis(PrEP) if you’re at risk for HIV.
  • Don't share personal items. Touching germs on drinking glasses, eating utensils, toothbrushes, razors and combs can lead to illness.
  • Travel wisely. Talk to your doctor about any special vaccinations if you’re traveling — particularly if you’re leaving the country.


Signs and symptoms vary depending on the specific disease, but often include fever, diarrhea, fatigue or muscle aches.

Your primary care doctor may admit you to the hospital if you:

  • Have been bitten by an animal or insect.
  • Are having trouble breathing.
  • Have been coughing for more than a week.
  • Have severe a headache with a fever.
  • Experience a rash or swelling.
  • Have an unexplained fever.
  • Have sudden vision problems.


To understand what's causing your symptoms, your doctor may order diagnostic tests such as:

  • Blood or urine test.
  • Throat swab.
  • Stool sample.
  • Spinal tap (lumbar puncture).

Your doctor may also use imaging exams — such as X-rays, CT or MRI— to rule out other conditions that may be causing your symptoms. Or, your doctor may ask for a biopsy, a tiny sample of tissue taken from an internal organ for testing. For example, a biopsy of lung tissue can be checked for fungi that cause pneumonia.


Infectious disease doctors are trained in the use of antibiotics and their side effects, immunology (how the body fights infection), epidemiology (how infections spread) and infection control. Once your doctor finds the cause of your illness, he or she will determine the appropriate treatment.

Treatment may include:

  • Antibiotics. Your doctor may prescribe an antibiotic for an infectious disease caused by bacteria, keeping in mind that several types of bacteria have developed resistance to some varieties of antibiotics.
  • Antivirals. This type of medication can treat a small number of viruses, including those that cause AIDS, herpes, hepatitis B or hepatitis C, and influenza (flu). 
  • Antifungals. Antifungals fight fungal infections that may affect the lungs or the mucous membranes of the mouth and throat, often found in people with weakened immune systems.
  • Antiparasitics. Diseases, such as malaria, that are caused by parasites may be treated with antiparasitic medications. Similar to certain antibiotics, some antiparasitics aren’t effective on varieties of parasites that have developed resistance to these drugs.