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.

OHSU monitoring report: Infectious diseases in Oregon

OHSU COVID Forecast cover image.

OHSU’s lead data scientist, Peter Graven, Ph.D., provides regular updates on COVID-19, fluRSV and other infectious diseases.

Media: Call 503-494-8231 or email

  • COVID hospitalizations have steadily fallen for two months after peaking at the start of October. 
  • COVID deaths, positive tests and wastewater detection are falling in Oregon. They are rising in other regions, though, as  part of a clear fall-winter wave.
  • Low levels of flu are reported in Oregon and most of the U.S.
  • RSV is rising in Oregon, spiking in other states, and has peaked in Georgia.
  • COVID is likely to begin a new wave in Oregon soon. Most other states are seeing increases, though levels will probably be moderate like last year. The peak is likely in late December or early January.
  • RSV’s peak could arrive in two or three weeks. Based on patterns in other states, it could be similar to last year’s.
  • The flu season appears to be later than last year. It may follow a more common pattern of increasing in December and peaking in January or February. The level is not expected to be higher than usual.

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

    The CDC warned Nov. 23 that measles vaccination rates are at their lowest since 2008 and that millions of children worldwide are at risk of infection. 

      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)

      The U.S. last had a mumps outbreak in 2019, with 3,780 cases. Thirty-six states have reported at least one mumps case in 2022; Oregon has reported five.

      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

      A case of paralytic polio was reported in New York state in July 2022 in an unvaccinated young adult.

      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.

      More than 100 OHSU staffers helped care for an Oregon boy who got tetanus in 2019.

      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.
        • Use our MD 4Kids app to help:
          • Decide whether a child needs care.
          • Treat a child’s symptoms that can be managed at home.

        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 a:

          • Flu vaccine
          • COVID-19 vaccine
          • Jynneos vaccine (mpox)
          • Many other vaccines

          Download the MD 4KIDS app

          A graphic of a rag doll under which reads "OHSU" and "MD 4KIDS," comprising the logo of the OHSU Doernbecher MD 4KIDS health information library app.