Infectious Diseases: Causes and Treatments

An adult puts a hand on a child’s forehead while taking her temperature with a digital thermometer in her mouth.

What are infectious diseases?

Infectious diseases happen when germs enter our bodies and cause infections. Germs include:

  • Bacteria
  • Viruses
  • Parasites
  • Fungi

Some, but not all, infectious diseases are contagious. That means they spread person to person.

Common infectious diseases

Some infectious diseases are or have been common enough that we routinely vaccinate people against them, typically in infancy and childhood. 

Chickenpox, a viral disease, causes an itchy and sometimes painful rash on the whole body. Chickenpox spreads easily to people who haven’t had it or weren’t vaccinated against it.

The virus that causes chickenpox also causes another painful rash called shingles. The shingles vaccine is recommended for:

  • People 50 and older
  • People 19 and older with weakened immune systems (immunocompromised)

This bacterial infection often damages tissues in the nose and throat. If it gets into the blood, it can damage the heart, nerves and kidneys. It can also infect the skin. Diphtheria spreads through droplets from coughing or sneezing.

This viral disease damages the liver. The most common types are called hepatitis A, hepatitis B and hepatitis C. Vaccines are available for hepatitis A and B. Hepatitis can spread through:

  • Eating or drinking something that contains even a microscopic amount of stool from an infected person who didn’t wash their hands.
  • Sharing personal items, such as toothbrushes or razors.
  • Sharing needles, syringes and other medical items.
  • Sex with an infected person.
  • Being born to an infected person.

About 97,800 people get hepatitis each year in the U.S. Hepatitis B and C can become chronic (ongoing) conditions and can cause liver cancer.

This viral disease has symptoms that include:

  • High fever
  • Cough
  • Conjunctivitis (eye swelling or infection)
  • Rash

This viral disease spreads through close contact, especially repeated contact. Symptoms include:

  • Fever
  • Headache or muscle aches
  • Tiredness
  • Lack of appetite
  • Swollen salivary glands (cheeks and jaw)

This contagious viral disease has symptoms that vary from person to person:

  • No visible symptoms (most people)
  • Flu-like symptoms (about one in four people)
  • Serious symptoms such as:
    • Meningitis, an infection of the brain or spinal cord
    • Weakness or paralysis (can’t move) in the arms, legs or both

In most people, this viral disease causes mild symptoms. But in unvaccinated pregnant people, it can cause a miscarriage or serious birth defects.

This bacterial infection makes muscles tighten, especially in the jaw, which can cause breathing and swallowing problems. Tetanus does not spread from person to person. People usually get tetanus through broken skin.

This bacterial infection starts like a cold. In children and adults, it moves to violent coughing fits that can last up to 10 weeks. These coughing fits can cause:

  • A high-pitched “whoop” sound
  • Vomiting
  • Tiredness
  • Trouble breathing

Babies may not cough. Instead, they may:

  • Struggle to breathe
  • Turn a bluish or gray tint (depending on skin color)
  • Stop breathing briefly (apnea)

Unvaccinated pregnant people should get the whooping cough vaccine to protect their babies, who cannot get it until 2 months. A CDC study released in February 2023 found that vaccinations during pregnancy helped prevent  whooping cough cases in newborns. The CDC recommends getting the vaccine between the 27th and 36th weeks of pregnancy. 

Preventing infectious diseases

OHSU experts say the best way to avoid infectious diseases is to keep up with vaccines. Children’s doctors offer vaccines against certain infectious diseases on a standard schedule that starts at birth.

Many pharmacies offer vaccines for flu and COVID-19. It’s safe to get both at the same time. OHSU pharmacies also offer the Jynneos vaccine for mpox. 

Find a flu shot or COVID-19 vaccine near you:                                                      

Learn about an RSV vaccine for people 60 and older and who are pregnant; and an RSV medication for infants.

You can limit the spread of infectious diseases by:

  • Washing hands often.
  • Staying home if you have symptoms.
  • Avoiding crowds.
  • Cleaning and disinfecting commonly used surfaces often.
  • Covering coughs and sneezes.
  • Wearing masks in indoor public spaces.

You can get more than one infectious disease at the same time (co-infections). People who get co-infections may:

  • Have more serious symptoms.
  • Be at higher risk of:
    • Complications
    • Other infections

Diagnosing infectious diseases

Infectious diseases have similar symptoms and signs. Your provider can order lab tests to figure out what you have.

For respiratory viruses like RSV, flu and COVID-19, lab tests usually mean doing a nose or throat swab.

Lab tests may also use samples of:

  • Blood
  • Saliva
  • Stool
  • Urine

Care and treatment of infectious diseases

For mild symptoms or if you think you need a test:

  • Contact your provider.
  • Get same-day care in person or virtually.

These symptoms need medical care right away, especially in babies and children:

  • Trouble breathing or swallowing
  • Chest pain
  • Severe muscle pain
  • Dehydration (dark yellow urine or not urinating for more than eight hours)
  • Seizures
  • High fever (above 104 degrees) or any fever in a baby younger than 3 months (12 weeks)
  • Not alert or interacting with other people
  • Bluish or gray tint on lips or face (depending on skin color)
  • Chronic (ongoing) medical condition that gets worse

Care at OHSU

Vaccines at OHSU

Make an appointment for:

  • Jynneos vaccine (mpox)
  • RSV
  • Shingles
  • Many other vaccines