5 Most Common Infectious Diseases

Various kinds of diseases can be found everywhere around the globe, with thousands of them are highly infectious. With the aftermath of COVID-19, it is easy to forget the existence of more common diseases still lingering about, ready to infect people.

There’s a good reason to be anxious about several infectious diseases since some may even have fatal consequences when left untreated.

Here are five of the most common you might encounter:

Tick-Borne Diseases

Bacteria and viruses are not the only causes of illnesses – parasites like ticks play a role in spreading dangerous pathogens across various organisms, including humans.

Tick-borne illnesses are amongst the most common infectious diseases, especially in warmer regions. A tick infected with bacteria, viruses, and other parasites may bring dangerous conditions like the following:

  • Lyme Disease – The most common illness acquired from deer tick after it bites the skin and stays latched on for 48 hours. Symptoms may include a bulls-eye rash at the site of infection, flu-like symptoms, and arthritis and carditis in the long term.

To avoid Lyme Disease, avoid wooded areas, fields, overgrown grass fields, lawns, and gardens.

  • Babesiosis – Though this disease is unknown, babesiosis is severe and requires immediate medical attention. Caused by babesia microti, symptoms include fever, chills, sweats, headache, nausea, fatigue, body aches, and loss of appetite, although some may not feel anything. They may also cause hemolytic anemia and may be fatal for immunocompromised people from other causes (AIDS, lymphoma, cancer), lacking a spleen, the elderly, or those with existing serious illnesses.

Foodborne Illnesses

Poorly prepared food can become a host for many infectious diseases, usually from bacteria. You’ve heard of people getting food poisoning from infected meals, with the most typical symptoms being diarrhea, fever, stomach cramps, and vomiting.

From its source to preparation, contaminated food can carry dozens of diseases, some of which include the following:

  • Coli – This bacterium comes from the intestinal tract and can infect through contaminated meat and water.

  • Hepatitis A – Arguably the most common foodborne infection. Fortunately, a vaccine exists to prevent spreading.

  • Salmonella – Usually contracted from infected food and water. Salmonella is the most frequently reported case in the United States.

  • Norovirus – Often reported on cruise ships, is highly contagious and the common cause of gastroenteritis.

  • Campylobacter – A common diarrheal illness contracted from animals, animal products, or even pets.

Staphylococcus Infection or Staph

One common infectious disease overshadowed by the COVID-19 pandemic is Staph. Caused by the Staphylococcus bacteria, this germ is found on the skin or noses of relatively healthy people. Staph infections remain highly prevalent, despite the lack of news of infection cases.

Symptoms of Staph include the following:

  • Skin infections – Staph manifests on the skin, often as boils, cellulitis, impetigo, and Staphylococcal scalded skin syndrome, with the last symptom mostly affecting babies and children.

  • Food poisoning symptoms like nausea, vomiting, dehydration, low blood pressure, and diarrhea.

  • Bacteremia – also referred to as bloodstream infection. It occurs when staph bacteria enter the bloodstream and affect the brain, lungs, and heart, causing meningitis, pneumonia, and endocarditis; bones, muscles, and surgically implanted devices like pacemakers. Signs include fever and low blood pressure.

  • Septic arthritis – staph bacteria target the knees, hips, shoulders, fingers, and toes. Symptoms include fever, swelling of affected joints, and severe joint pain.

  • Toxic shock syndrome – is a life-threatening condition occurring when the bacteria releases toxins and suddenly develops with a high fever, confusion, muscle ache, stomach pain, sunburn-like rashes on the palms and soles, nausea and vomiting, diarrhea, and high fever.

Sexually-Transmitted Diseases (STDs)

A rising concern, sexually-transmitted diseases affect many sexually-active individuals. STDs are transmitted through sexual contact and bodily fluids like vaginal secretions or semen.

These can be avoided by using protection like condoms, abstaining from sex, or medically testing partners for prior infections.


The most common STD, chlamydia, is often diagnosed in men and women between 20-25 years old. This illness can be transmitted via having sex with an infected partner (even if they do not ejaculate) or pregnancy (pregnant women can pass it to their child).

Symptoms of chlamydia include:

  • Abnormal vaginal discharge

  • Discharge from penis

  • Aches and swelling in one or both testicles

  • Burning sensation when peeing

  • Rectal pain, discharge, and bleeding


While syphilis is not as prevalent as chlamydia, this illness has serious long-term effects, causing four progressive stages that can be fatal if left untreated. Syphilis is spread through a syphilis sore during anal, vaginal or oral sex.

This can also be transmitted via physical contact with everyday objects like toilet bowls, doorknobs, and shared utensils.

Syphilis symptoms are divided into four stages:

Primary Stage

The primary stage manifests syphilis as a sore or multiple sores in the following areas:

  • Lips or in the mouth

  • Penis

  • Vagina

  • Rectum

Secondary Stage

  • Rough, red to reddish brown rashes in the same areas where the sores were or on the palms or soles

  • Fever

  • Swollen lymph nodes

  • Headaches

  • Patchy hair loss

  • Sore throat

  • Weight loss

  • Muscle pain

  • Fatigue

Latent Stage

During the latent stage, there are no physical symptoms, but syphilis may remain in the body.

Tertiary Stage

Most people with syphilis do not develop tertiary syphilis. Still, once it happens, it will attack various organ systems like the heart, blood vessels, brain, and nervous system. The tertiary stage occurs 10-30 years after infection and may result in death. An STI may use various tests to determine whether or not a patient has tertiary syphilis.

Additional: Neurosyphilis, Ocular Syphilis, and Otosyphilis

At any stage, untreated syphilis can spread to the brain and nervous system, causing symptoms such as:

  • Neurosyphilis – muscle weakness, changes in mental state (personality change, confusion, focus issues), dementia, severe headaches

  • Ocular syphilis – eye pain, eye redness, poor vision, or blindness

  • Otosyphilis – tinnitus, hearing loss, vertigo, dizziness

Influenza (Flu)

When it comes to common infectious diseases, influenza disease tops the charts. This respiratory virus is spread through respiratory droplets exhaled by infected individuals. Influenza is seasonal, and some of the most common include:

  • Influenza A virus (IAV) – spread from animals to humans, responsible for influenza pandemics

  • Influenza B virus (IAB) – spreads between humans and shares the same symptoms as influenza B. IBV is most common from September to April.

  • Influenza C virus (IAC) – the least severe, mildest form of flu

Flu symptoms manifest as follows:

  • Chills

  • Cough

  • Sore throat

  • Headaches

  • Fatigue

  • Runny nose and cough

  • Fever

Preventing the Spread of Diseases

Fortunately, many of these common infectious diseases can be prevented through proper hygiene and practicing responsibility. Washing your hands and disinfecting can help you avoid contracting many infections, and vaccines can act as added protection.

You can thank your immune system for providing the much-needed protection you need, but when you’re a patient in a hospital waiting to be treated, you might need more than just staying clean. Hospitals use hundreds of tools and equipment daily, all of which must be completely decontaminated to keep patients safe.

When protecting patients from bacteria, viruses, parasites, and fungi from medical instruments, sterile processing technicians are the professionals. They are the unsung heroes of the allied healthcare industry, and if you want to learn more about them, visit Martinson College today.

Read More: Different Common Methods of Disinfection