Infection happens when microorganisms enter the body and grow. The body may respond in different ways depending on the type of infection and the extent of it. One or more of the following microorganisms can cause an infectious disease:

• Viruses
• Bacteria
• Parasites
• Fungi

Infectious diseases can range from common illnesses, such as the cold, to serious illnesses, such as acquired immune deficiency syndrome (AIDS). Depending on the specific illness and where you live, an infectious disease can spread in some or all of these ways:

• Sexual transmission. It's spread through sexual contact, including intercourse.
• Airborne transmission. It's spread through inhaling airborne droplets of the disease. These may exist in the air as a result of a cough or sneeze from a person who is sick.
• Blood-borne transmission. It's spread through contact with infected blood, such as when sharing hypodermic needles.
• Direct skin contact. It's spread through contact with the skin of a person who is sick.
• Insect-borne transmission. It's spread through insects, such as mosquitoes. These draw blood from a person who is sick and then bite a healthy person.
• Foodborne transmission. It's spread through consuming contaminated food.
• Waterborne transmission. It's spread through contact with contaminated water.
• Other mechanisms that can spread a disease.

In pregnancy, problems from infections are common. You may be more prone to the effects of infection during pregnancy because your immune system is naturally suppressed. Certain infections may cause problems for the fetus (developing baby) and may endanger your health. Some organisms that do not usually cause problems for people can be dangerous when you're pregnant. Other organisms are not harmful when you're pregnant. But they can be harmful to the fetus.

The symptoms of an infection often depend on the organism causing the infection. Also, infection in pregnancy may or may not have obvious symptoms. Or during pregnancy, a person may show different symptoms of an infection. The symptoms may look like other conditions or health problems. Always see your doctor for a diagnosis.

The diagnosis of an infection depends on the symptoms and a history of exposure to the organism. Certain tests are done as part of routine prenatal care to rule out common infections. Some tests help determine your immunity to an infectious disease, such as rubella. Other tests, such as blood tests, cultures, or tissue samples, are used only when needed for diagnosis.

You and your doctor will figure out the best treatment based on:

• Your overall health and past health.
• The type of infection.
• The specific medicines, procedures, or therapies that are safe during pregnancy.
• The risks and benefits of treatment to you and your baby.
• How long the condition is expected to last.
• Your opinion or preference.

Some infections, such as urinary tract infections, may not be preventable. Prevention of other infections depends on how they are spread. You can reduce your risk of getting some infectious diseases by not coming into contact with the infecting organism. For example, toxoplasmosis, which is found in cat feces, may be prevented by not having contact with litter boxes and by having good hand washing practices. Sexually transmitted infections can be prevented by not having sexual contact with an infected partner and by practicing safer sex.

The Zika virus is transmitted by infected mosquitoes. It can be transmitted from a person to their fetus. You can also get Zika from sexual intercourse with someone infected with Zika.

To help prevent infection with the Zika virus:

• Do not travel to areas with Zika.
• If you must travel, follow steps to prevent mosquito bites while on your trip.
• Speak with your doctor before your trip.

If your partner lives in an area with Zika or has traveled to an area with Zika, use condoms every time you have sex during the pregnancy.