Nature of DiseaseNature of DiseaseIntroduction - DefinitionsNormal Bacteria & Host

Koch’s PostulatesPatterns of DiseaseSpread of Infection

Nosocomial Infections

Disease - IntroductionDisease - Introduction

Pathogens - disease causing with special properties that permit host invasion

Disease - when microorganism overcomes host defenses; an abnormal physiological state

Pathology - the study of disease

Disease - IntroductionDisease - Introduction

Infection - invasion & growth of pathogen in host; systemic vs. localized

Pathogenesis – the study of the development of disease

Etiology – the study of the cause of disease

Disease - Normal BacteriaDisease - Normal Bacteria

Animals - germ free in utero but are colonized almost immediately after birth

Different bacteria are normally associated with different parts of body

Transients - microorganisms that may occasionally be found associated with the host

Disease - Normal BacteriaDisease - Normal Bacteria

Skin– S. epidermidis/S. aureus

Gastrointestinal Tract– Gram negative bacteria (large

intestine)– Streptococcus. mutans (mouth)

Genito-Urinary Tract– Lactobacillus

Disease - Normal BacteriaDisease - Normal Bacteria Antagonism - normal bacteria prevent

growth of others Bacteria and host have symbiotic

relationship (living together) Three types of symbiosis

– Commensalism (one benefits)– Mutalism (both benefit)– Parasitism (one benefits & other harmed)

Opportunistic - do not cause disease normally

Disease - Koch’s Disease - Koch’s PostulatesPostulates Etiology or cause established using

Koch’s postulates– same pathogen present in every

instance of disease– pathogen isolated in pure culture– isolated pathogen causes disease

when reintroduced into a healthy host– pathogen re-isolated from the now

diseased host

Disease - PatternsDisease - Patterns

Predisposing factors make hosts more susceptible & include:– age– gender– climate– level of fatigue– nutrition

Disease - Patterns - Disease - Patterns - DevelopmentDevelopment Incubation period - time between

infection & first signs Prodromal period - first mild signs Illness period - period when all

symptoms are present Decline period Convalescence period

Disease - Spread of Disease - Spread of InfectionInfection Reservoirs of Infection

– a continuing source of infection Reservoirs include:

– Human - people who have disease or are carriers (infected but no symptoms)

– Zoonoses - wild or domestic animals that transmit disease to humans

– Nonliving - soil & water

Disease - Spread of Disease - Spread of InfectionInfection Transmission

– Direct contact– Fomites - inanimate objects– Droplet - saliva, mucus coughing or

sneezing– Medium - food, water air– Airborne - carried > 1 meter– Arthropod - insect vectors

Disease - Nosocomial Disease - Nosocomial InfectionInfection Acquired during hospitalization or a stay in other health care facilities

Occurs at 5-15% Can be normal organisms

introduced into wrong part of body during invasive procedures

Opportunitic drug resistant G-, e.g. Pseudomonas

Disease - Nosocomial Disease - Nosocomial InfectionInfection Compromised host

– burns– wounds– immune suppressed (disease or

drugs) Chain of Transmission

– Direct contact– Fomites

Disease - Nosocomial Disease - Nosocomial InfectionInfection Control

– Aseptic techniques– Proper cleaning storage– Maintenance– Properly trained staff

Problems– Multiple drug resistance– Nonuse of effective cleaning agents– Training of staff