There are five stages of infection, each with a different duration and symptoms. These differences also depend on the type of infection.

Infection occurs when an organism, such as a virus or bacterium, invades the body. The infectious agent rapidly multiplies in the body’s tissues. Although not all infections result in disease, some can trigger the immune system, causing symptoms of illness.

There are five stages of infection:

  • incubation
  • prodromal
  • illness
  • decline
  • convalescence

This article will explain each of the five stages of infection in detail, describing how long they can last and giving examples of infections.

It will also highlight what the stages of infection are, specifically in people with HIV.

a pharmacist is working in a drug storeShare on Pinterest
Luis Alvarez/Getty Images

The incubation stage includes the time from exposure to an infectious agent until the onset of symptoms.

Viral or bacterial particles replicate during the incubation stage.


The exact time frame of the incubation stage varies depending on the infection. Here are a few examples:


The flu virus incubates for 1–4 days, but symptoms can appear as early as 2 days after the virus enters the body.

Hepatitis B

The incubation period for hepatitis B virus (HBV) ranges from 1.5–6 months.


Salmonella, a common foodborne bacterium, causes symptoms within 6 hours to 6 days. They can include:

The prodromal stage refers to the period after incubation and before the characteristic symptoms of infection occur.

People can also transmit infections during the prodromal stage.

During this stage, the infectious agent continues replicating, which triggers the body’s immune response and mild, nonspecific symptoms. These symptoms can include:


The duration of the prodromal stage varies depending on the type of infection.

For example, the flu has a short incubation period of about 2 days. As a result, the prodromal stage may overlap with the incubation stage and the onset of illness.

The Centers for Disease Control and Prevention (CDC) state that the virus might transmit to others 1 day before symptoms develop and up to a week after becoming ill.

The third stage of infection is an illness or clinical disease. This stage includes the time when a person shows apparent symptoms of an infectious disease.


The symptoms of infection vary widely depending on the underlying cause.

In general, people who have an active infection may experience:

Respiratory infections

Symptoms of respiratory infections, such as the common cold or influenza, include:

Gastrointestinal infections

Gastrointestinal infections can cause the following symptoms:


The exact time frame varies depending on the type of infection, the number of infectious microbes in the body, and the strength of a person’s immune system. Here are some examples:


Symptoms can last up to a week for many viral respiratory infections, such as the flu.

Hepatitis B

Certain infections can last several weeks or even years. Symptoms of hepatitis B can last several weeks. It can also develop into a chronic disease if the infection continues for more than 6 months.

Chickenpox, herpes

The herpes simplex virus (HSV) and chickenpox (VZV) can hide in a dormant state within nerve cells. These viruses can stay in the body for many years before reactivating. If the VZV virus reactivates, it causes shingles.

Chickenpox symptoms usually last between 4 and 7 days.

Herpes symptoms vary in their duration depending on the type of infection.

During the decline stage, the immune system mounts a successful defense against the pathogens, and the number of infectious particles decreases.

Symptoms will gradually improve.

However, a person can develop secondary infections during this stage if the primary infection has weakened their immune system.

During this stage, the virus can still transmit to other people.

The final stage of infection is known as convalescence.

During this stage, symptoms resolve, and a person can return to their normal functions.

Depending on the severity of the infection, some people may have permanent damage even after the infection resolves.

HIV damages the immune system. If left untreated, HIV progresses into AIDS. Exposure to HIV occurs when a person comes in contact with body fluids that contain HIV particles.

The CDC list three stages of HIV:

Stage 1: Acute HIV infection

These early stages of HIV infection are also known as acute HIV infection. HIV spreads throughout the body and attacks specialized white blood cells, called CD4+ T cells.

Stage 2: Chronic HIV infection

If left untreated, acute HIV infection progresses to chronic HIV, which can last for decades.

In chronic HIV, the virus continues to replicate and destroy CD4 cells. People may not experience symptoms at this stage. However, the absence of symptoms does not mean that the infection is gone.

Stage 3: AIDS

If a person with chronic HIV does not receive treatment, they can develop AIDS.

At this point, the virus has significantly weakened the immune system, leaving the body vulnerable to other infections.

If AIDS is left untreated, a person typically survives for about 3 years.

Infection typically occurs in five stages.

The incubation stage occurs right after exposure and before symptoms develop. This stage can range from hours for some infections to days, weeks, or even years for other infections.

The next stage is prodromal, which involves mild, nonspecific symptoms.

During the illness stage, a person shows the characteristic symptoms of infection, such as a rash in chickenpox or vomiting due to food poisoning.

The decline stage occurs when the number of infectious microbes declines and symptoms resolve.

The final stage is convalescence. During this stage, symptoms disappear, and the body starts to recover.

HIV has three stages of infection: acute, chronic, and AIDS.