Infection happens when germs (like bacteria, viruses, fungi and parasites) invade and grow inside your body where they don’t belong. The infection can be localized in one area or spread throughout the whole body and symptoms vary depending on the type of infection. Most infections are mild and can be treated at home, but some, such as the flu, pneumonia, strep throat, gonorrhea and tuberculosis, can be serious.
Germs can spread when a sick person coughs or sneezes, releasing tiny droplets that contain the germs. These droplets can land on other people and infect them when they touch their eyes, mouth or nose. Alternatively, the germs can stick to surfaces like door handles, toys or tables and contaminate them. Other ways that germs spread include direct contact with contaminated fluids such as urine, faeces, saliva and breastmilk and through bug bites.
Bacteria are the most common causes of infection and are associated with diseases such as strep throat, tuberculosis, skin infections (such as acne) and urinary tract and bloodstream infections. Viruses cause many of the same types of infections as bacteria and may also be more severe, such as the flu and measles. Fungi can cause infections of the skin and soft tissues, such as tinea corporis and tinea pedis (ringworm and athlete’s foot), and parasites can be either internal (such as pinworm and giardia) or external (such as lice and scabies).
Immunocompromised patients are at greater risk for infection because their immune systems don’t react as quickly to pathogens. These patients often have atypical symptoms, making diagnosis difficult. New tests using metagenomics sequencing, which detects all of the organism’s DNA, offer promise as a more accurate and timely method to diagnose infection.