Infection is when there is overgrowth of microorganisms (like bacteria, viruses and fungi) somewhere in the body. This overgrowth may result in symptoms like pain, swelling, fever and redness.
The body’s natural defense systems usually fight off infectious organisms, but sometimes the immune system can get overwhelmed. Then, the infection can become harmful or even life-threatening.
Viruses and bacteria are the most common causes of infections in humans. Viruses can cause infections in different parts of the body, such as the genitals or the respiratory tract. Symptoms of a viral infection include a runny nose, cough and body aches.
Bacteria are microscopic single-celled organisms that look like balls or rods under a microscope. They are found everywhere in nature and on the body. Most bacteria do not make people sick, and some are even helpful, such as the “good” bacteria in your digestive tract that help digest food and absorb nutrients. Some bacteria produce toxins that can attack and kill cells or spread from one cell to another, making people sick.
Infections caused by bacteria can be spread through direct contact with infected skin or mucous membranes, droplets or particles in the air (like phlegm or snot), or through contaminated food or water or from a bug bite (like ticks and mosquitoes). Some bacteria cause bacterial diseases that can spread between people, such as impetigo and boils, or that are passed from mother to baby during childbirth (genital infections). Other bacteria, such as those that cause Legionnaire’s disease, pertussis (whooping cough) or tuberculosis, spread from person to person or through contaminated water or food (vehicular). These diseases often have serious or even fatal consequences.
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