Bacterial Infections

How bacterial infections happen

Bacteria are single-celled organisms. Most of those living on and in us are harmless or helpful. Infection occurs when disease-causing bacteria get past the body's defenses, multiply and damage tissue, either directly or by releasing toxins. They enter through:

• breaks in the skin (cuts, bites, surgery)
• the airways (droplets from coughs and sneezes)
• the gut (contaminated food or water)
• the urinary or genital tract
• medical devices such as catheters

Common types of bacterial infection

Bacterial vs viral infections

Mucus color alone does not tell you whether an infection is bacterial. Yellow or green phlegm is common in viral infections. Tests help when the cause is unclear.

Symptoms

Symptoms depend on where the infection is:

• General: fever, chills, sweats, tiredness, aches
• Local: pain, redness, warmth and swelling; pus or discharge
• Organ-specific: burning urination (UTI), sore throat with swollen tonsils (strep), cough with phlegm and chest pain (pneumonia), diarrhea and cramps (gut infections)

Diagnosis

Doctors often diagnose common infections from symptoms and examination. Tests confirm the bacteria and guide antibiotic choice:

• Rapid tests and swabs: strep tests, wound and genital swabs
• Urine tests and cultures
• Blood tests: white cell count, CRP and procalcitonin (markers of inflammation), and blood cultures in serious infection
• Imaging: chest X-ray for pneumonia, ultrasound or CT for abscesses
• Cultures and sensitivity testing: grow the bacteria in a lab and check which antibiotics work

Treatment

Antibiotics

Antibiotics kill bacteria or stop them multiplying. The choice depends on the likely bacteria, the site, local resistance patterns, allergies and test results. Key points:

• take them exactly as prescribed, for the full course your prescriber recommends
• many common infections need shorter courses than in the past; follow current advice
• never take leftover or someone else's antibiotics
• tell your doctor about allergies, pregnancy and other medicines
• common side effects include diarrhea, nausea, rash and yeast infections

Some mild infections, such as uncomplicated ear infections in older children and many sinus infections, clear on their own, and doctors may suggest watchful waiting.

Other treatment

• Draining abscesses, which antibiotics alone often cannot cure
• Removing infected devices such as catheters
• Supportive care: fluids, rest, and fever and pain relief such as acetaminophen (paracetamol) or ibuprofen, following the label dose. Do not give aspirin to children or teenagers
• Hospital care with intravenous antibiotics for severe infections and sepsis

Antibiotic resistance

When antibiotics are used unnecessarily or incorrectly, bacteria can evolve to survive them. Resistant infections such as MRSA and drug-resistant gonorrhea or tuberculosis are harder to treat. You can help by using antibiotics only when a clinician recommends them and never demanding them for colds or flu.

Prevention

• wash hands with soap and water
• keep vaccinations up to date: pneumococcal, pertussis (Tdap), meningococcal, Hib and others
• clean and cover wounds
• cook food thoroughly and avoid cross-contamination
• practice safer sex
• prevent tick bites with repellents and checks after outdoor activities

Frequently asked questions

What are the signs of a bacterial infection?

Signs include fever, localized pain, redness, warmth and swelling, pus, symptoms that persist beyond 10 days, or symptoms that improve and then worsen. The exact symptoms depend on which part of the body is infected.

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

It is often difficult without a test. Viral infections usually cause runny nose, cough and aches that peak within a few days and improve. Bacterial infections are more often localized, with pus, high fever, or worsening after initial improvement. A doctor can test when needed.

Can bacterial infections go away without antibiotics?

Some mild ones can, such as many ear and sinus infections, because the immune system clears them. Others, such as UTIs with fever, strep throat, cellulitis and pneumonia, need antibiotics to prevent complications. Ask a clinician rather than waiting with worsening symptoms.

What is the most serious complication of a bacterial infection?

Sepsis, an extreme body-wide response to infection that can damage organs and be fatal. Warning signs include confusion, fast breathing, a racing heart, very high or low temperature, and cold, mottled skin. It needs emergency treatment.