Short answer
Infection means an infectious agent has entered and multiplied in the body. Disease means the person has an illness or impaired health. Some infections produce clear illness; others are asymptomatic. Cancer and diabetes illustrate diseases that are not infections. 1 2
An infection can cause infectious disease, but infection can exist without noticeable disease, and many diseases are not infectious.
On this page
At a glance
Scroll to compare all columns →
| Question | Infection | Disease |
|---|---|---|
| Core question | Is an infectious agent established? | Is health impaired or illness present? |
| Can occur without symptoms? | Yes | A disease may be diagnosed before obvious symptoms, but is a health condition |
| Requires a microbe? | Yes, in this scope | No |
The table summarizes the cited definitions and the article’s stated scope. 1 2
What each thing is
Infection. The entry and multiplication of an infectious agent in a host, with a biological response. 1
Disease. A state of impaired health or illness; in this article, especially illness caused by infection. 2
Key differences
A microbe or virus can be present without producing noticeable symptoms, and a disease can arise through noninfectious processes. Clinicians distinguish exposure, colonization, infection and disease; those stages are related but not identical. Here infection refers to the process involving an agent and a host response. 1 2
How to tell them apart
Ask whether evidence shows an agent established in the host, and separately whether there is illness or impairment. A positive test may support infection without proving that the person’s current symptoms have that cause. Diagnosis depends on the relevant test and clinical context. 1 2
Where they overlap
Many infectious diseases begin with infection. Fever, inflammation and tissue injury can accompany both the biological infection process and the resulting clinical disease. 1 2
Edge cases
An asymptomatic person can still have an infection. A disease can be subclinical or diagnosed before the person feels sick; therefore “disease means symptoms” is too rigid. Colonization without infection is another boundary requiring context. 1 2
Why the distinction exists
Public health counts infections and cases of illness differently because the two answer different questions about spread, burden and care. 1 2
Common misconceptions
Every infection is not automatically a symptomatic disease, and every disease is not caused by a germ. 1 2
Examples
A person tests positive for an infectious virus yet feels well: infection without noticeable illness. A person with a noninfectious inherited condition has a disease without an infection. 1 2
Sources
Sources checked October 3, 2026.
- Centers for Disease Control and Prevention — Infection Control Basics. Overview and colonization.
- CDC NERD Academy — Glossary. Infection, disease, pathogen and asymptomatic entries.