Diseases Produced by Bacteria: Different Types and Statistics of the Ability of These Microorganisms to Affect Our Body

The most common conditions caused by these microorganisms include meningitis, gastritis, and sexually transmitted diseases, among others.

A substantial number of infections are caused by species of bacteria that are present in or in many people without causing disease.

Very often, these bacteria only become pathogenic when they end up in a place where they are not supposed to be or when their numbers have increased excessively due to a weakening of the immune system.

However, there are also strains of bacteria that always cause disease, such as the enterohemorrhagic strains of the bacterium Escherichia coli.

The bacteria responsible for the most common conditions

Steotococci pneumonia

Often called “pneumococci,” these bacteria are generally present in the nose and pharynx of many people without causing any infection.

Therefore, the healthy carriers in the population transmit the bacteria to the elderly, children, or other susceptible people, among whom a severe illness can appear.

In Switzerland, pneumococci cause about a thousand serious infections (in the bloodstream or as meningitis) each year and several thousand cases of pneumonia.


These bacteria are also responsible for many independently resolving infections, such as bronchitis and ear infections.

La Staphylococcus aureus

It is present as part of the skin flora in about one-third of the human population without causing disease depending on the strain and immune system of the infected person.

S. aureus can infect the skin, bones, and soft tissues within the body, including the bloodstream. In hospitals, it is the most common cause of postoperative infections.

In animal husbandry, it can trigger various infections, particularly in the udders of dairy cows (mastitis).

La Escherichia coli

It is an enterobacterium that lives in the intestines of humans and animals without causing disease. It is even helpful and part of healthy individuals’ normal intestinal flora.

But it can cause infections if it goes to another part of the body, such as the lower urinary tract, abdomen, or brain in newborns.

Certain pathogenic strains of E. coli (e.g., toxin-producing O157: H7) are known to pass from animals to humans through food products.

In humans, these bacteria can cause fever, nausea, vomiting, stomach cramps, and diarrhea, which can be fatal in some cases.

La Klebsiella pneumoniae

It is another species of Enterobacteriaceae commonly present in the digestive tract of healthy humans and animals.

However, it is one of the most common culprits for causing hospital-associated infections and urinary and respiratory tract infections, especially pneumonia.

In newborns, Klebsiella pneumonia can infect the bloodstream, leading to increased mortality rates. This type of bacteria also can easily acquire multiple forms of antibiotic resistance.

Also worth mentioning is Acinetobacter baumanni I and Pseudomonas aeruginosa, which are among the so-called hospital pathogens, as they mainly cause infections in hospitals and care homes.

The resistance of these two bacterial species to last-resort antibiotics, such as carbapenems and polymyxins, is increasing nationally and globally.

The main reportable diseases

In Switzerland, a mandatory notification system allows doctors and laboratories to declare certain infectious diseases to the Medical Director of each canton of the Federal Office of Public Health (FOPH).

This report allows early detection of potential public health problems and, therefore, also early preventive measures if necessary.

There are more than 40 different diseases on the list of reportable diseases.

The number of cases reported annually shown below is estimated based on the previous three years’ average for bacterial infections that must be registered.

Airborne Bacterial Agents

  • Pneumococci: invasive diseases, about 900 cases reported per year.
  • Tuberculosis: around 500 reported cases per year.
  • Legionella: about 400 reported cases per year.
  • Haemophilus influenzae (a type of bacteria that has nothing to do with the virus responsible for the flu): invasive diseases, about 100 cases reported per year.
  • Meningococci: invasive infections, approximately 50 issues reported per year.

Orally transmitted bacterial agents

  • Campylobacter: about 7,500 reported cases per year.
  • Salmonella: about 1,500 reported cases per year.
  • Enterohemorrhagic E. coli infections: about 600 reported cases per year.
  • Shigella: about 150 reported cases per year.
  • Listeria: about 50 reported cases per year.
  • Typhoid and paratyphoid fever (S. Typhi, S. paratyphi): 20 reported cases per year.

Bacterial agents are transmitted sexually or through contaminated blood.

  • Chlamydia: about 11,000 reported cases per year.
  • Gonorrhea: about 2,400 reported cases per year.
  • Syphilis: about 1,000 reported cases per year.

Bacterial agents transmitted by animals

  • Lyme disease (borreliosis): about 10,000 reported cases per year.
  • Tularaemia: about 80 reported cases per year.
  • Brucellosis: less than ten reported cases per year.