Carrier is a person who harbors the pathogenic microorganism without suffering from any disease from it.
Classification:

1. Healthy carriers: These are the persons who harbor the microorganism bud had never suffered from any disease by it.

2. Convalescent carriers: These are the persons who had been infected by that microorganism and are recovering from that infection. Even though they have no more symptoms of the disease, they continue to shed the microorganism into the environment.

3. Temporary carriers: The carrier state lasts for less than 6 months.

4. Chronic carriers: the carrier state extends beyond 6 months and may even last for years.

5. Contact carrier: A person can become a contact carrier when he acquires the microorganism due to his contact with the patient.

6. Paradoxical carrier: A person is a paradoxical carrier when he acquires the microorganism from another carrier.

Sites of carriage:

1. Nasal: Staphylococcus aureus

2. Nasopharyngeal: meningococcus, Bordetella

3. Urinary: Salmonella

4. Fecal: Salmonella

5. Serum: hepatitis B

6. Hands: Klebsiella, Pseudomonas, Staphylococcus

Importance: Carriers are often a risk to the public health as they have the potential to infect others. Many outbreaks have known to occur due to carriers. Example:"Typhoid Mary"- Mary Mallon had caused a small outbreak of typhoid wherever she served as maid. Children who get infected early in life become Hepatitis B carriers and have high risk of progression to hepatocellular carcinoma. In hospitals, if the health care personnel is a carrier, then that person may become a source of infection to many hospitalized patients. Those individuals are nasal carriers (of S.aureus) tend to have frequent infections.
Detection of carriers:

1. Culture:

•Nasal carriage of S.aureus by culture of nasal swab.
•Urinary carrier of Salmonella by repeated urine culture.
•Fecal carrier of Salmonella by repeated stool or bile culture.


2. Serologic detection:

•Serum HbsAg detection for hepatitis B carrier
• Detection of Vi antibody in serum for Salmonella carrier.
• Detection of carriers in society by 'sewer swab' technique.

Eradication of carrier state: Carrier state can be eradicated by long term antibiotic usage. Mupirocin, neomycin are used to prevent carrier state of S.aureus. Rifampin is used to prevent carrier state of meningococci. Cholecystectomy may be sometimes required to eradicate carrier state of Salmonella. However, carrier state of Hepatitis B cannot be eradicated.