Carrier or Subclinical State

People can be "carriers" of certain agents, which means that they do not show symptoms of illness but they can effectively transmit the agent to others. Since only a portion of the ill population exhibits symptoms with these types of illnesses, the number of clinically ill is not the same as the total number of people who are actually infected. The proportion of infected people who have symptoms, varies greatly by disease. The carrier state can be either transient, or persistent and chronic.

The carrier state can manifest in the following ways:

• The person is asymptomatic (showing no symptoms) while infected, but is infectious. • The person is still in the incubation period for illness, and will develop symptoms at a later date, but is already infectious. • The person is infectious after symptoms have resolved.

For example, people infected with hepatitis A are infectious for approximately 2 weeks before they develop symptoms (during the incubation period) and continue to be infectious for approximately one week after they develop jaundice (a symptom of hepatitis A).   The period of greatest communicability is during the incubation period before symptoms develop. In children, HAV infections often may not result in clinical disease, but they can still transmit infection, especially during diaper changes, as hepatitis A is spread through fecal- oral transmission.

Jaundice due to hepatitis A infection