Also called: Communicable diseases
Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.
About Infectious Diseases
Germs, or microbes, are found everywhere - in the air, soil, and water. There are also germs on your skin and in your body. Many of them are harmless, and some can even be helpful. But some of them can make you sick. Infectious diseases are diseases that are caused by germs.
There are four main types of germs:
- Bacteria are one-celled germs that multiply quickly. They may give off toxins, which are harmful chemicals that can make you sick. Strep throat and urinary tract infections are common bacterial infections.
- Viruses are tiny capsules that contain genetic material. They invade your cells so that they can multiply. This can kill, damage, or change the cells and make you sick. Viral infections include HIV and the common cold.
- Fungi are primitive plant-like organisms such as mushrooms, mold, mildew, and yeasts. Athlete's foot and yeast infections are common fungal infections.
- Parasites are animals or plants that survive by living on or in other living things. Malaria and head lice are infections that are caused by parasites.
There are many different ways that you can get an infectious disease, depending on the type of germ. They can include:
- Through direct contact with a person who is sick. This includes kissing, touching, sneezing, coughing, and sexual contact. If you are pregnant, you can pass some germs to your fetus.
- Through indirect contact, when you touch something that has germs on it. For example, you could get germs if someone who is sick touched a door handle, and then you touch it.
- Through insect or animal bites.
- Through contaminated food, water, soil, or plants.
Infectious diseases can cause many different symptoms. Some are so mild that you may not even notice any symptoms, while others can be life-threatening.
There are treatments for some infectious diseases, such as antibiotic, antiviral, antifungal and anti-parasitic medicines. But for other infections, such as some caused by viruses, you can only treat your symptoms while you wait for your immune system to fight off the germ.
You can take steps to help prevent many infectious diseases:
- Get vaccinated.
- Wash your hands often.
- Pay attention to food safety.
- Avoid contact with wild animals.
- Use a latex condom every time you have sex. If your or your partner is allergic to latex, you can use polyurethane condoms.
- Don't share items such as toothbrushes, combs, and straws.
It sits within Infections and Immune System.
The lead U.S. institute for this subject is the National Institute of Allergy and Infectious Diseases.
When to speak to someone. Reading about a topic cannot tell you whether it applies to you. Speak to a doctor or pharmacist if symptoms are severe, sudden, getting worse, or simply not going away — and seek emergency care immediately for chest pain, breathing difficulty, sudden weakness or confusion, or a serious allergic reaction.
Research on Infectious Diseases
23,637 studies areregistered for this condition on ClinicalTrials.gov, the U.S. National Library of Medicine's public registry. A selection is below — the links go straight to the registry entry, not to a summary of ours.
What a registered study does and does not mean. Registration means a study exists and has been declared publicly. It says nothing about whether the treatment being tested works, is safe, or is available to you. Many studies find no benefit — that is what research is for. Never seek out an experimental treatment on the strength of a registry entry alone.
Research currently under way
- A Study to Learn About the Study Medicine Ibuzatrelvir in Adults With COVID-19 Who Are Severely ImmunocompromisedPfizer
- Long-term Follow-up of Long-acting Cabotegravir (CAB LA) for PrEP (Pre-exposure Prophylaxis) in Participants at Risk of Acquiring HIV (Human Immunodeficiency Virus)ViiV Healthcare
- Screening for LID Clinical Studies Unit Healthy Volunteer ProtocolsNational Institute of Allergy and Infectious Diseases (NIAID)
- Allogeneic Hematopoietic Cell Transplantation for Peripheral T Cell LymphomaNational Cancer Institute (NCI)
- Study to Evaluate the Efficacy, Safety, and Tolerability of Long-acting Intramuscular Cabotegravir and Rilpivirine for Maintenance of Virologic Suppression Following Switch From an Integrase Inhibitor in HIV-1 Infected Therapy Naive ParticipantsViiV Healthcare
- A Study to Evaluate the Use of Resmetirom in Participants With MASLD and HIVNaga P. Chalasani
Research already completed
- Increasing PrEP Use in High-Risk Social Networks of African-American MSM in Underserved Low-Risk CitiesMedical College of Wisconsin
- Effects of Immulina TM Supplements With PASC PatientsUniversity of Mississippi Medical Center
- Study of the Safety of a Particular Herpes Vaccine in Adults With or Without Herpes InfectionNational Institute of Allergy and Infectious Diseases (NIAID)
- The Effect of HPV Education Provided to Women on Their Knowledge Levels, HPV Screening, and Vaccination UptakeUfuk University
- Spirulina Oral Supplement for Enhancing Host Resilience to Virus InfectionUniversity of Mississippi Medical Center
- Randomised Clinical Trial in Treatment Modalities for Cutaneous Leishmaniasis Caused by Leishmania Tropica, in PakistanMedecins Sans Frontieres, Netherlands
Study data from ClinicalTrials.gov, a service of the U.S. National Library of Medicine. Retrieved 2026-07-30. Registry entries are supplied by study sponsors and investigators; ClinicalTrials.gov does not verify their scientific validity. PocketsInfo is not affiliated with, and not endorsed by, the NLM or the NIH.
Where to read more
Rather than paraphrase, we point you to the primary sources. Every link below is to a government health agency, a national institute or a recognised medical body — grouped by what you are trying to find out.
Start Here
- Germs: Understand and Protect against Bacteria, Viruses, and InfectionsMayo Foundation for Medical Education and Research
- Infectious DiseasesMayo Foundation for Medical Education and Research
Diagnosis and Tests
- PCR TestsNational Library of Medicine
- Rapid TestsNational Library of Medicine
Prevention and Risk Factors
- Germs and Hygiene: MedlinePlus Health TopicNational Library of Medicine
Living With
- Coping with Stress during Infectious Disease OutbreaksSubstance Abuse and Mental Health Services Administration
- Taking Care of Your Behavioral Health: Tips for Social Distancing, Quarantine, and Isolation during an Infectious Disease OutbreakSubstance Abuse and Mental Health Services Administration
Related Issues
- About Port HealthCenters for Disease Control and Prevention
- Antibiotic Resistance: MedlinePlus Health TopicNational Library of Medicine
- Bacterial vs. Viral Infections: How Do They Differ?Mayo Foundation for Medical Education and Research
- Recurrent Infections May Signal ImmunodeficienciesAmerican Academy of Allergy, Asthma, and Immunology
- What's the Difference Between Infectious and Contagious?Nemours Foundation
Statistics and Research
- FastStats: Infectious DiseaseNational Center for Health Statistics
Clinical Trials
- ClinicalTrials.gov: Communicable DiseasesNational Institutes of Health
Medical subject headings
Clinicians and researchers index this subject under Communicable Diseases. These are the terms to use when searching medical literature.
This page is built from the MedlinePlus health topic record for Infectious Diseases, a service of the U.S. National Library of Medicine (NLM), National Institutes of Health. Information is from MedlinePlus.gov. PocketsInfo is not affiliated with, and is not endorsed by, the NLM or the NIH. Retrieved 30 July 2026.