Infectious Diseases

Overview

What are infectious diseases?

Infectious diseases can be caused by many pathogens, including bacteria, viruses, fungi, and parasites that may cause illness and disease. For humans, transmission of pathogens may occur in a variety of ways: spread from person-to-person by direct contact, water or foodborne illness or aerosolization of infected particles in the environment and through insects (mosquitoes) and ticks.

Signs and symptoms and treatment of infectious diseases depend on the host and the pathogen.

Who is most at risk for getting infectious diseases?

Anyone can get an infectious disease. People with a compromised immune system (an immune system that doesn’t work at full strength) have greater risk for certain types of infections. Those at higher risk include:

  • People with suppressed immune systems, such as those going through cancer treatment or who have recently had an organ transplant
  • Those who are unvaccinated against common infectious diseases
  • Healthcare workers
  • People traveling to at-risk areas where they may be exposed to mosquitoes that carry pathogens such as malaria, dengue virus and Zika viruses.

How common are infectious diseases?

Infectious diseases are extremely common worldwide. Some infectious diseases strike more often than others. For instance, in the United States, 1 out of every 5 people is infected with the influenza (flu) virus each year.

What complications are associated with infectious diseases?

Many infectious diseases cause complications. These can range from mild to severe. For some conditions, complications may include wheezing, skin rash, or extreme fatigue. Mild complications usually disappear as the infection resolves.

Certain infectious diseases may cause cancer. These include hepatitis B and C (liver cancer), and human papillomavirus (HPV) (cervical cancer).

Symptoms and Causes

What are the symptoms of infectious diseases?

Symptoms of infectious disease are particular to the type of disease. For example, symptoms of influenza include:

Other infectious diseases, such as Shigella, cause more serious symptoms, including:

  • Bloody diarrhea
  • Vomiting
  • Fever
  • Dehydration (lack of fluid)
  • Shock

You may experience one or several symptoms of an infectious disease. It’s important to see a doctor if you have any chronic (ongoing) symptoms or symptoms that get worse over time.

What causes infectious diseases?

Infectious diseases in humans are caused by microorganisms including:

  • Viruses that invade and multiply inside healthy cells
  • Bacteria, or small, single-celled organisms capable of causing disease
  • Fungi, which include many different kinds of fungus
  • Parasites, which are organisms that live inside host bodies causing sickness

Infectious diseases spread in multiple ways. In many cases, direct contact with a sick individual, either by skin-to-skin contact (including sexual contact) or by touching something another person touches, transmits the disease into a new host. Contact with body fluids, such as blood and saliva, also spreads infectious diseases.

Some diseases spread through droplets discharged from a sick person’s body when they cough or sneeze. These droplets linger in the air for a short period of time, landing on a healthy person’s skin or inhaled into their lungs.

In some cases, infectious diseases travel through the air for long periods of time in small particles. Healthy people inhale these particles and later become sick. Only certain diseases spread with airborne transmission, including tuberculosis and the rubella virus.

Diagnosis and Tests

How are infectious diseases diagnosed?

Doctors diagnose infectious diseases using a variety of laboratory tests. Samples of blood, urine, stool, mucus or other body fluids are examined and provide information used in the diagnostic process.

In some cases, doctors identify infectious organisms by examining them under a microscope. Occasionally, laboratories must grow, or culture, the infectious organism from a sample to confirm its presence.

Management and Treatment

How are infectious diseases treated?

Treatment depends on which microorganism causes the infection.

  • If bacteria cause a disease, treatment with antibiotics usually kills the bacteria and ends the infection.
  • Viral infections are usually treated with supportive therapies, like rest and increased fluid intake. Sometimes people benefit from antiviral medications like oseltamivir phosphate (Tamiflu®).
  • Doctors treat fungal and parasitic infections with antifungal medications, like fluconazole (Diflucan®), and antiparasitic drugs, such as mebendazole (Emverm®).

In all cases, doctors treat specific symptoms of infectious diseases according to the latest medical guidelines. Talk with your doctor about your symptoms to explore possible treatment options.

Prevention

Can infectious diseases be prevented?

Vaccines are available to prevent many common infectious diseases, including hepatitis, diphtheria, influenza and herpes zoster. The CDC has updated recommendations for vaccinations for children, adolescents and adults. There are new platforms for delivery of vaccinations and research on new pathogens. It is also important to consult with a travel clinic prior to travel overseas to be sure you are protected.

You can also reduce your risk of contracting an infectious disease by:

  • Washing your hands with soap and water, thoroughly and frequently
  • Covering your nose and mouth when you sneeze or cough
  • Disinfecting frequently touched surfaces in your home and workplace
  • Avoiding contact with sick people or sharing personal items with them
  • Not drinking or swimming in contaminated water supplies
  • Not eating or drinking food and beverages prepared by people who are sick

Outlook / Prognosis

What are the outcomes after treatment for infectious diseases?

With treatment, most people recover fully from infectious diseases. Some infectious diseases, like HIV (human immunodeficiency virus), cannot be cured yet. Instead, doctors focus on symptom management and preventing the disease from progressing further.

Increasingly, antibiotic medications may not be effective against certain infectious diseases. Gonorrhea, a sexually transmitted infection affecting both men and women, is usually treated with antibiotics. Recently, doctors have identified drug-resistant strains of the bacteria that causes gonorrhea. These resistant strains are much less likely to respond to treatment with antibiotics. It’s important to seek care from a doctor who can help you find the right therapy for a persistent infection.

Living With

When should I call my doctor concerning an infectious disease?

Let your doctor know if you have any symptoms of an infectious disease, especially if they are unusual or don’t go away over time. Symptoms like fever, vomiting and diarrhea may lead to more serious complications, including dehydration.

Your doctor should also know if you plan to travel to foreign countries. You may need to be vaccinated against common infectious diseases occurring at your destination.

If you have an ongoing infection, frequent follow-ups with your doctor help ensure your condition does not worsen.

Last reviewed by a Cleveland Clinic medical professional on 02/27/2018.

References

  • World Health Organization. Accessed 3/6/2018.Infectious Diseases. (http://www.who.int/topics/infectious_diseases/en/)
  • United States Department of Labor. Accessed 3/6/2018.Infectious Diseases. (https://www.osha.gov/SLTC/healthcarefacilities/infectious_diseases.html)
  • National Institute of Allergy and Infectious Diseases. Accessed 3/6/2018.Diseases & Conditions: Infectious Diseases. (https://www.niaid.nih.gov/diseases-conditions/infectious-diseases)
  • National Foundation for Infectious Diseases. Accessed 3/6/2018.Influenza (Flu). (http://www.nfid.org/influenza)
  • Merck Manual Consumer Version. . Accessed 3/6/2018.Diagnosis of Infectious Disease (http://www.merckmanuals.com/home/infections/diagnosis-of-infectious-disease/diagnosis-of-infectious-disease)

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