Infectious Disease: Causes, Symptoms, and Treatment
Medically reviewed by Harsha Moole, MD, Internal Medicine. Last reviewed: October 2, 2026.
What kind of doctor treats Infectious Disease?
Most infections are treated first by a primary care doctor. When an infection is unusual or does not respond to standard treatment, the doctor may refer the patient to an infectious disease specialist. A direct primary care or concierge doctor can be a first stop for an evaluation and can refer you to a specialist when needed.
What is an infectious disease?
An infectious disease is an illness caused by germs such as bacteria, viruses, fungi, or parasites. These germs can spread from person to person, through food or water, or from insects and animals. Some infections are mild and go away on their own. Others need treatment from a doctor.
Infectious diseases happen when germs enter the body and start to grow. Common examples include the flu, COVID-19, strep throat, urinary tract infections, and pneumonia. The immune system usually clears the infection, but sometimes medicine or other care is needed.
Symptoms
Symptoms depend on the germ and the body part affected. Common signs include fever, tiredness, coughing, sore throat, diarrhea, and muscle aches. Some infections also cause a rash, swelling, or pain in one area.
Causes and who gets it
Infectious diseases are caused by bacteria, viruses, fungi, and parasites that enter the body through the mouth, nose, skin, or other routes. Risk is higher in babies, older adults, and people with weak immune systems, and poor handwashing raises it further.
How doctors diagnose it
Doctors start by asking about symptoms and doing a physical exam. They may order blood work, a urine test, a throat swab, or imaging like a chest X-ray to identify the germ and choose the right treatment.
Treatment
Treatment depends on the germ. Bacterial infections are treated with antibiotics, while antiviral or antifungal medicines are used for some other infections. Many mild infections get better with rest, fluids, and over-the-counter medicine.
When to see a doctor
Anyone with a high fever, trouble breathing, chest pain, severe headache, confusion, or a stiff neck should get medical care quickly. Call a doctor if symptoms last more than a few days or keep getting worse.
How a direct primary care or concierge doctor fits in
A direct primary care doctor charges a flat monthly fee instead of billing insurance; a concierge doctor usually charges more and often works alongside insurance. Either type can handle many common infections, order tests, prescribe medicine, and follow up closely, referring complex cases to a specialist.
Common questions
Do antibiotics treat every infection?
No. Antibiotics only work against bacteria, not against viruses like those that cause colds and the flu. Taking antibiotics when they are not needed can cause harm and make bacteria harder to kill in the future.
Are infectious diseases always contagious?
No. Contagious means the illness can spread from person to person. Some infections, like those from a tick bite or contaminated food, do not pass between people at all.
How can I lower my risk of getting an infection?
Washing hands often with soap and water helps a lot. Staying up to date on vaccines, handling food safely, and avoiding close contact with sick people also lower risk.
When is a fever a reason to worry?
A fever with trouble breathing, a stiff neck, confusion, or a rash needs quick medical care. Any fever in a baby younger than three months should be checked by a doctor right away.
Sources
Medical Disclaimer
This content is for general educational and informational purposes only and is not medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment, and reading it does not create a doctor-patient relationship. Always seek the advice of your physician or another qualified health provider with any questions about a medical condition, and never disregard or delay seeking professional advice because of something you read here. If you think you may have a medical emergency, call 911 (or your local emergency number) immediately.
