Transmission of disease

Disease transmission In a nursing context one of the major aims is to prevent infection. So for every episode of infection…… • 1) Where did the organism come from? • 2) How did it get there? Reservoirs of Infection • A reservoir is the “original” source of the organism, not necessarily the most recent. • Where the organism normally lives and multiplies. Reservoirs for Human Disease Humans animals environment Human reservoirs endogenous versus exogenous Infected people symptomatic asymptomatic carriers Incubation period true Convalescent phase Normal flora Infect somebody else Infect yourself (endogenous) Endogenous infection What conditions can produce an endogenous infection? • Change in host defenses / physiology. • Change in site of the organism. • Change in number of the organism. More reservoirs of infection Animals Normal flora infected Same disease Different disease Environment Especially the soil, but also water. Portals of exit and entry • Where the organism LEAVES one host and ENTERS another. - usually identical in both hosts. - can be different. - some organism have multiple portals. • Portal of entry can modify disease. • Portal of entry can also modify communicability Direct and Indirect Transmission Direct transmission Reservoir New host Indirect transmission Reservoir Vehicle (non living) Food, water, fomites intermediate New host Vector (living) mechanical biological Shigella faeces fingers flies food New host Hepatitis B semen Body fluids Blood donation needle New host Transmission through air • Droplet nuclei - about 1m - DIRECT. • Airborne - more than 1m - longer time span - air now becomes a vehicle. - INDIRECT Bloodborne infections • Relatively non communicable due to portal of entry and exit. • HIV, Hep B and C, arboviruses. Mechanisms of transmission • Blood transfusion, IV inoc • Insects • Cutaneous inoculation (needlestick) Common source outbreaks • Same infection in many people acquired via common exposure. • Compare with a propogated outbreak. • Food and water are often implicated as common source vehicles. Diseases in a population • Sporadic, endemic or epidemic • Morbidity, mortality, prevalence, incidence Level of infection is governed by • Infectivity of organism (dose required) • Level of exposure (means of transmission) • Susceptibility of the population.