Epidemiology & Nosocomial Infections-Lesson 14

Aetiology is a specialization in microbiology in which the cause of disease is studied. Epidemiology is the study of the spread of disease.

The incidence is the number of cases seen in a year. The prevalence is the number of people infected at any one time. Morbidity is used to report the number of cases/100,000 people/year and mortality is used to report the number of deaths/100,000 people/year.

A sporadic disease usually has a fairly small number of isolated cases, such as meningitis. An endemic disease is constantly present in the population but the incidence and severity is quite low, such as chicken pox (prior to vaccine development). An epidemic disease usually has a very high incidence and very often a high mortality rate as well, such as influenza from time to time. A pandemic disease is a world-wide epidemic, as in Cholera. A zoonotic disease is transmitted from animals to humans, for example, rabies.

The entry point of an infectious microbe is called the portal of entry. This is typically a break in the skin or entry through one of the many mucous membranes in the body. If transmission of the pathogen is going to occur, the infectious agent must leave the host at what is known as a portal of exit. Generally this includes bodily fluids or solid waste.

Contact transmission includes direct contact (horizontal direct meaning physical contact or vertical direct meaning mother to offspring), indirect contact by fomites (inanimate objects) or droplet transmission (respiratory secretions). Vehicle transmission occurs by exposure to contaminated water, air or food. Vector transmission can be due to a mechanical or biological vector.

A reservoir of disease is a site where the infectious microbe can maintain its ability to infect. Reservoirs are commonly animals or human carriers.

When you begin to immunize various members of the community, the incidents of disease is greatly lowered

Nosocomial infections are those that are transmitted in a hospital or other medical environment.

The sources of pathogens can be exogenous, meaning from the environment, and might include staff, other patients or visitors as well as fomites. Another source of pathogens can be endogenous, meaning from the patient's own normal flora which leads to an opportunistic infection.

The most common nosocomial pathogen is Escherichia coli which is responsible for many urinary tract diseases. Staphylococcus aureus is responsible for skin and wound diseases, often as a post-surgical complication, whereas Pseudomonas aeruginosa is often a skin pathogen in burn units. Various species of Streptococcus are responsible for respiratory diseases such as Pneumonia.

Any surgical procedure creates a portal of entry, increasing the risk of infection. Also, patients in the medical environment tend to be debilitated with a depressed immunity.

Good quality control measures must be in place to screen for these pathogens, especially the highly drug resistant ones. Also, aseptic procedures must be in place and followed diligently. Finally, the appropriate use of antibiotics should be carried out but the indiscriminate use should be avoided at all costs, to limit the spread of multi-drug resistant strains of nosocomial pathogens.

False. Staphylococcus aureus is responsible for skin and wound diseases, often as a post-surgical complication

True

True