Types of Infections

 
Infection is invasion and multiplication of microorganism in a host, it does not always cause disease. Disease will not occur if the host’s immunity is active.

Parasites are those microorganisms which can establish themselves and multiply in the hosts. Parasites can be pathogens (pathos (G) =suffering; gen=causing) or commensals (com= sharing ; mensa=table; sharing table=living together)

Pathogens are microorganisms that can produce disease in a host. The process of attacking the host and causing disease is known as pathogenesis.

Commensals are microorganisms that live in a state of harmony with the host, without causing any damage. The normal bacterial flora of the body are largely commensals. They maybe facultative pathogens, causing disease if the immunity of the host is lowered.

A disease resulting from an infection is an infectious disease.

Infections can be of many types

Primary Infection – It is the first or initial infection caused by a parasite/microorganism in a host.
Re-infection – Subsequent infections by the same parasite in the host. For example, a malaria can come again/recur in an individual if exposed to it repeatedly.

Secondary Infection - A new microorganism/parasite causes an infection in a host already suffering from a pre-existing infection and has lowered immunity, it is a secondary infection eg; fungal infection following pulmonary tuberculosis in a patient

Focal Infection/Focal sepsis- infection/sepsis at a particular site eg; appendicitis, tonsilitis. Does not spread to other places.

Iatrogenic Infections- Physician induced infections- resulting from different investigative, diagnostic or other procedures in a hospital eg, abscess/deep wound after an injection

Nosocomial Infections- Hospital acquired infections- Health care associated infections (HAI)

Depending on the Source of infection

• ·    Endogenous Infection – If source of infection is from within the host’s own body – eg. Peritonitis- following intestinal injury, if gut flora causes infection

• ·       Exogenous infection- If source of infection is from outside the host’s own body

Depending on the clinical effects of infection,

• ·       Inapparent/Subclinical Infection- where clinical symptoms of infection are not seen

• ·       Atypical Infection- where the characteristic/typical clinical symptoms are not seen

• ·   Latent Infection -where some microorganisms, after the infection, remain hidden in the tissues in a latent/dormant form. They produce disease when the host immunity is lowered/compromised, later.

Cross Infection - If a patient already suffering from an infection gets another infection from another host or any other external source, it is a cross infection. Infections acquiring from hospitals are due to cross infection.