Incubation Period

The incubation period (from Latin incubo — to brood, to rest) is a defined interval from the initial entry of a pathogenic microorganism into the human body to the onset of the first clinical symptoms of the disease.

Etiology and pathophysiology

During the incubation period, the individual subjectively feels healthy; however, an extensive pathological process is already developing at the cellular level. During this time, the pathogen overcomes physical barriers (the skin, mucous membranes, and the acidic environment of gastric juice) and reaches specific target cells.

After penetrating the tissues, the virus or bacterium begins to multiply actively (replicate). Clinical symptoms are absent because the concentration of the pathogen or the toxins it produces has not yet reached the critical threshold (infectious dose) required for extensive cellular damage or the initiation of a systemic inflammatory response.

The duration of this stage varies among infections:

• from several hours — in foodborne toxicoinfection;
• up to several weeks — in chickenpox or hepatitis B;
• up to several years — in prion diseases.

Clinical significance

The duration of the incubation period is a fundamental epidemiological parameter. It forms the basis for determining the duration of quarantine and medical observation of contacts.

From a clinical perspective, the latent period is an ideal “window of opportunity” for emergency prophylaxis.

For example, if an individual has had contact with a patient with chickenpox or has been bitten by an animal with rabies, immediate administration of a vaccine and/or specific immunoglobulin during the incubation period helps the immune system eliminate the virus before it causes disease.

A particular epidemiological risk is that, in many respiratory diseases, the patient becomes highly contagious (infectious) during the final days of the incubation period and sheds the virus in saliva while still unaware of the disease.