Infection
When germs invade and multiply in the body, causing illness
Quick Facts
- Type: Infectious (caused by germs)
- Main causes: Bacteria, viruses, fungi, parasites
- Common signs: Fever, redness, pain, swelling, fatigue
- Seek urgent care: High fever, confusion, fast breathing, spreading redness
Overview
An infection occurs when microscopic organisms, often called germs, enter the body, multiply, and trigger a reaction. These germs include bacteria, viruses, fungi, and parasites. Infections can affect almost any part of the body, from the skin and lungs to the bloodstream, and they range from minor problems that clear on their own to serious, life-threatening illnesses.
The body's immune system normally fights off many invading germs, but sometimes the germ overwhelms these defenses or enters through a wound or weak point. Understanding the type of infection helps guide treatment, because the medicines that work against bacteria, for example, do not work against viruses. Some infections are contagious and spread between people, while others come from the environment or from germs that normally live harmlessly in the body but get out of balance.
Symptoms
Symptoms depend on the type of germ and the part of the body affected, but many infections share common features.
- Fever, chills, or sweating
- Redness, warmth, swelling, or pain at a local site, such as a wound or skin area
- Fatigue and a general feeling of being unwell
- Coughing, sore throat, or runny nose with respiratory infections
- Pain or burning when urinating with urinary infections
- Nausea, vomiting, or diarrhea with gut infections
- Pus or discharge from a wound or body opening
Warning signs of a serious or spreading infection include a very high fever, confusion, fast breathing or heartbeat, low blood pressure, and redness that spreads quickly. These can signal sepsis and need emergency care.
Causes
Infections are caused by different types of germs, each treated differently:
- Bacteria: Single-celled organisms that can cause illnesses such as strep throat, urinary infections, and some pneumonias; often treated with antibiotics.
- Viruses: Tiny germs that cause colds, flu, and many other illnesses; antibiotics do not work against them.
- Fungi: Cause infections such as athlete's foot, thrush, and some lung infections.
- Parasites: Organisms such as those causing malaria or intestinal worms.
Germs can spread through the air, by touch, through contaminated food or water, by insect bites, through wounds, or from person to person.
Risk Factors
- A weakened immune system from illness, medication, or chemotherapy
- Diabetes or other chronic diseases
- Open wounds, burns, or surgical sites
- Very young or older age
- Close contact with infected people or contaminated environments
- Medical devices such as catheters or implants
Diagnosis
Doctors diagnose infections based on symptoms, examination, and tests to identify the germ involved.
- Blood tests: To detect signs of infection and inflammation and sometimes the germ itself.
- Cultures: Samples of blood, urine, wound fluid, or sputum grown in a lab to identify the organism and which medicines will work.
- Imaging: X-rays, ultrasound, or scans to find infection in organs such as the lungs or an abscess.
- Swabs and rapid tests: For example, throat swabs or tests for specific viruses.
Identifying the exact germ helps doctors choose the most effective and appropriate treatment.
Treatment
Treatment depends on the type of germ and the severity of the infection.
- Antibiotics: For bacterial infections, chosen to match the bacteria; it is important to take the full course as directed.
- Antiviral medicines: For certain viral infections, though many viral illnesses improve with rest and supportive care.
- Antifungal and antiparasitic medicines: For fungal and parasitic infections.
- Supportive care: Rest, fluids, fever-reducing medicines, and treating symptoms.
- Drainage or surgery: For abscesses or infected collections that need to be drained.
Severe infections may require hospital care, intravenous medicines, and close monitoring. Using antibiotics only when needed helps slow the rise of antibiotic-resistant germs.
Prevention
- Wash hands regularly and thoroughly
- Keep wounds clean and covered
- Stay up to date with recommended vaccines
- Handle and cook food safely and use clean water
- Avoid close contact with people who are unwell when possible
- Take antibiotics only as prescribed and finish the full course
When to See a Doctor
See a doctor if you have a fever that lasts or rises, a wound that becomes red, swollen, or oozes pus, or symptoms that worsen instead of improving. Seek emergency care immediately if you or someone else has:
- A very high fever with confusion, drowsiness, or difficulty waking
- Fast breathing, a racing heart, or low blood pressure
- Redness that spreads quickly across the skin
- A stiff neck and fever, severe headache, or a rash that does not fade when pressed
- Signs of sepsis such as feeling extremely unwell with cold or mottled skin
Frequently Asked Questions
What is the difference between bacterial and viral infections?
Bacteria and viruses are different types of germs. Bacterial infections can often be treated with antibiotics, while viral infections cannot, and many viral illnesses improve with rest and supportive care. A doctor may run tests to tell them apart and choose the right treatment.
Why shouldn't I take antibiotics for every infection?
Antibiotics only work against bacteria, not viruses, so taking them for viral illnesses like colds does no good and can cause side effects. Overusing antibiotics also helps bacteria become resistant, making future infections harder to treat. Take antibiotics only when prescribed and finish the full course.
When does an infection become an emergency?
Seek emergency care if you have a very high fever with confusion or drowsiness, fast breathing or heartbeat, low blood pressure, rapidly spreading skin redness, or a stiff neck with fever. These can signal a serious, spreading infection or sepsis that needs urgent treatment.
How can I prevent infections?
Wash your hands regularly, keep wounds clean and covered, stay up to date with vaccines, handle food safely, and avoid close contact with people who are ill when possible. These simple steps greatly lower the risk of catching and spreading many infections.
Are all infections contagious?
No. Some infections spread easily between people, such as colds and flu, while others come from the environment, contaminated food, insect bites, or germs that normally live in the body but get out of balance. Whether an infection is contagious depends on the germ involved.
References
- Centers for Disease Control and Prevention (CDC). Infectious diseases.
- MedlinePlus, U.S. National Library of Medicine. Infections.
- World Health Organization (WHO). Infectious diseases overview.
- Mayo Clinic. Infectious diseases — Symptoms and causes.