Bacterial infections

What are bacterial infections? What causes them and what are the risk factors? How can they be prevented? Find all the answers to your questions in our health file on bacterial infections.

Posted on 23 Jul 2025

I. Definition and key figures

Bacteria are unicellular micro-organisms found in almost every environment: in soil, air, water, on human skin and in the intestine. They play an indispensable role in digestion and protection against other microbes. However, some bacteria can become pathogenic and cause disease, known as bacterial infections [1].

These infections can affect various organs: the skin, lungs, brain, urinary tract or digestive system. Symptoms vary depending on the infected organ and the type of bacteria, but can include fever, severe headache, nausea, vomiting, pain, inflammation, pus production or skin lesions such as abscesses or boils [2][3].

Key figures

According to the IHME, in 2019, 1 in 8 deaths worldwide were linked to bacterial infections, representing the second leading cause of death [4].

Sub-Saharan Africa was the region of the world with the highest mortality rate linked to bacterial infections, with 230 deaths per 100,000 inhabitants in 2019 according to the IHME [4].

In 2022, tuberculosis caused almost 1.3 million deaths worldwide, ranking as the second leading cause of infectious disease mortality, after COVID-19 [5].

II. Causes and risk factors

Bacterial infections are mainly transmitted by:

Direct or indirect contact: skin wounds, scratches or cuts can allow bacteria present on the skin or contaminated surfaces to penetrate [2].

Airborne: some bacteria are spread by droplets expelled when coughing, sneezing or even talking. This is the case with tuberculosis and many bacterial pneumonias [5][7].

Contaminated food and water: ingesting contaminated food or water can transmit bacteria responsible for diseases such as gastroenteritis or cholera [8].

Unprotected sexual intercourse: some bacteria are transmitted sexually, such as gonorrhea and syphilis [9].

Certain factors increase vulnerability:

A weakened immune system: infants, the elderly, patients with chronic illnesses or immunosuppression [2].

Limited hygiene conditions: for example, restricted access to drinking water [8].

Inappropriate use of antibiotics encourages the development and spread of resistant bacteria [10].

III. The most common bacterial infections

Skin infections

These include a number of conditions:

Impetigo: a paediatric infection pathology causing scabs and body lesions [2].

Furuncles and abscesses: deeper infections of hair follicles with pus formation [2].

Bacterial dermohypodermatitis: a skin infection causing chronic oedema and inflammation. In the most severe cases, this is known as necrotizing bacterial dermohypodermatitis, which can attack underlying tissues [2].

Tuberculosis

Chronic bacterial infection caused by the bacterium Mycobacterium tuberculosis. In 2023, some 8.2 million new cases were reported, a record since the WHO began monitoring the disease worldwide in 1995 [11]. Tuberculosis mainly affects the lungs, but can also spread to other organs. Infection occurs via the air when an infected person coughs or sneezes [5].

Bacterial meningitis

Bacterial meningitis occurs when bacteria invade the meninges, the membranes enveloping the brain and spinal cord. Bacterial meningitis is a medical emergency that can lead to severe neurological sequelae, and even death in the most serious cases. Warning signs include high fever, intense headaches, neck rigidity and sometimes sensitivity to light [3].

Bacterial pneumonia

Lungs infection caused by bacteria such as Streptococcus pneumoniae or Haemophilus influenzae. They occur when these germs enter the respiratory tract, causing inflammation of the pulmonary alveoli, which then fill with pus or fluid, leading to symptoms such as cough, fever, chest pain and breathing difficulties. Common in children, the elderly and the immunocompromised, they can be serious if not treated promptly [7].

Urinary tract infections (cystitis)

Inflammations of the bladder most often caused by bacteria, notably Escherichia coli. They cause pain when urinating, frequent urination and sometimes abdominal pain. Although benign in most cases, they require prompt treatment to avoid complications such as kidney infection [6].

Sexually transmitted infections (STIs)

Some bacteria are transmitted during unprotected sexual intercourse. These infections are sometimes asymptomatic, which encourages their spread. Some bacterial STIs can lead to serious complications, such as infertility. It is essential to protect yourself before every sexual encounter [9]. To find out more about contraception, click here to consult our dedicated health file.

Cholera

Acute diarrheal disease caused by ingestion of water or food contaminated by bacteria. It manifests itself as profuse diarrhea and vomiting, leading to severe dehydration that can be fatal without prompt treatment [8]. You can find out more about this infection in our health file dedicated to cholera by clicking here.

IV. Prevention of bacterial infections

Prevention is based on several individual and collective measures:

Hand hygiene: regular hand washing with soap and water considerably reduces the transmission of many bacteria [8].

Wound care: disinfect cuts and scratches immediately to avoid skin infections [2].

Food hygiene: drink clean water, wash fruits and vegetables thoroughly, and cook food at an adequate temperature [8].

Vaccination: certain bacterial infections such as tuberculosis and meningitis can be prevented by vaccination [5].

Protection during sexual intercourse: using a condom helps prevent the transmission of bacterial STIs [9].

Reasoned use of antibiotics: never take antibiotics without a doctor’s prescription, and avoid overuse. These precautions are essential to limit the emergence of resistant bacteria [10].