Infection: Signs, Types and Treatment

How infections happen

Germs enter through breaks in the skin, the mouth, nose, eyes, airways, gut, urinary tract or genitals. Whether they cause infection depends on the type and amount of germ and the strength of your defenses. The immune system responds with inflammation, which causes many of the symptoms: redness, heat, swelling, pain and fever.

Types of infection

Antibiotics do not work against viruses. Using them when not needed causes side effects and antibiotic resistance.

Signs of infection

Local signs

• redness that may spread
• warmth
• swelling
• pain or tenderness that increases rather than settles
• pus or cloudy discharge
• a bad smell
• a wound that opens or does not heal

Signs of infection in a cut or wound

A healing wound is usually a little pink and tender for a few days. Signs of wound infection include redness extending more than about 1 to 2 cm (half an inch) from the edges, increasing pain after day 2 or 3, swelling, warmth, pus, red streaks and fever. Cuts on the lip, hand and foot, bites, and deep puncture wounds are more prone to infection.

Body-wide (systemic) signs

• fever or low temperature
• chills and shivering
• tiredness and aches
• swollen lymph nodes near the infected area
• loss of appetite, nausea

Signs an infection is spreading

• Expanding redness: draw a line around the edge with a pen; if it spreads beyond the line within hours, seek care. This is common in cellulitis.
• Red streaks: lines running from the wound toward the body, such as from the foot up the leg or from the hand up the arm. This is lymphangitis and needs prompt antibiotics.
• Swollen, tender lymph nodes in the groin, armpit or neck.
• Fever and chills.
• Severe pain, dusky or blistered skin: may indicate necrotizing fasciitis, a rare emergency.
• Signs of sepsis (see triage).

Dental infections and facial swelling

A tooth abscess can spread into the soft tissues of the face, causing facial cellulitis: swelling, redness and pain in the cheek, jaw or under the eye. Spread under the jaw or into the neck can block the airway. Facial swelling from a dental infection needs same-day care.

Genital infections in men

Infections of the penis, urethra, testicles or prostate can come from sexually transmitted infections (chlamydia, gonorrhea, herpes, syphilis), urinary infections or skin infections. Signs include discharge, burning on urination, sores, redness and swelling, and testicular pain. See male genitalia infection and sexually transmitted infections.

Sepsis

Sepsis is the body's extreme, life-threatening response to infection, damaging its own organs. It can start from any infection, including pneumonia, urinary tract infections, skin infections and abdominal infections. Older adults, babies, pregnant women, and people with diabetes, cancer, kidney disease or weakened immunity are at higher risk. Early treatment with antibiotics and fluids saves lives, so do not wait if signs appear.

Who is at higher risk of infection

• babies and older adults
• people with diabetes, kidney or liver disease, cancer or HIV
• people taking chemotherapy, steroids or other immune-suppressing medicines
• people without a working spleen
• people with wounds, burns, catheters or recent surgery
• people with poor circulation or skin breaks on the feet

Diagnosis

Many infections are diagnosed from symptoms and examination. Tests include:

• swabs of wounds, throat or discharge for culture or PCR
• urine tests
• blood tests: white cell count, CRP, blood cultures
• rapid tests for strep, flu and COVID-19
• imaging such as X-rays, ultrasound or CT to find deep infections or abscesses

Treatment

• Bacterial infections: antibiotics chosen for the likely germ; take the full prescribed course. Abscesses often need draining.
• Viral infections: rest, fluids, and fever relief; antivirals for flu, COVID-19, herpes and some others in specific situations.
• Fungal infections: antifungal creams, sprays or tablets.
• Parasitic infections: specific antiparasitic medicines.
• Supportive care: acetaminophen (paracetamol) or ibuprofen at the label dose for fever and pain; do not give aspirin to children or teenagers.
• Severe infections and sepsis: hospital care with IV antibiotics, fluids and organ support.

Prevention

• Wash hands with soap and water regularly.
• Clean cuts promptly with running water, cover them, and keep them clean and dry.
• Keep vaccinations up to date, including tetanus, flu, COVID-19 and pneumococcal vaccines as recommended.
• Practice safe food handling.
• Use condoms and get tested for sexually transmitted infections.
• Look after your feet if you have diabetes.
• Stay home when sick and cover coughs and sneezes.

Frequently asked questions

What are the signs of infection in a cut?

Signs include redness spreading from the edges, warmth, swelling, increasing pain after the first 2 to 3 days, pus or cloudy fluid, a bad smell, red streaks, and fever. A little pinkness and tenderness in the first days is normal healing.

How do I know if an infection is spreading?

Warning signs are redness that expands, red streaks moving from the wound toward the body, swollen tender glands, fever and chills, and feeling increasingly unwell. Draw around the redness to track it. Spreading infection needs prompt medical treatment.

How can I tell if an infection is bacterial or viral?

It is often hard to tell from symptoms alone. Viral infections like colds tend to affect several areas and improve within a week. Bacterial infections may be more localized, produce pus, or worsen after initial improvement. A doctor may use tests to decide if antibiotics are needed.

What are the warning signs of sepsis?

Warning signs include confusion, slurred speech, fast breathing, a very fast heart rate, shivering or fever, cold or mottled skin, very little urine, and feeling as if you might die. Call 911 or your local emergency number immediately if you suspect sepsis.

When should I see a doctor for an infection?

See a doctor if redness or swelling is spreading, there are red streaks, pus, increasing pain, fever, or the infection is on the face, hands, feet or genitals. People with diabetes, weakened immunity, babies and older adults should seek care sooner.