Infection is the invasion of foreign organism into human body. Human body will fight against the foreign organism with the help of immune system. This results in development of symptoms. Infection is a general term referring to any invasion caused by any type of organism. There are few types of organisms which can cause infections which are bacteria, virus, fungi, and parasites. The effects following infection varies according to the organ involved and the type of organisms causing the infection. It is worth to highlight that not all organisms cause infection because there are already a few types of organisms which are living in the human body and does not cause any symptoms or harm unless the immune system of the person goes haywire for example in an immunocompromised patient. There are few ways to identify the type and species of the organism that caused the infection. Investigations such as blood, urine, stool or sputum culture are able to identify the culprit.