nsi 2 Flashcards
w i Reservoir
and examples
habitat in which the agent normally lives, grows, and multiplies. Reservoirs include humans, animals, and the environment
wi a carrier
is a person with inapparent infection who is capable of transmitting the pathogen to others.
wi Asymptomatic or passive
healthy carriers are those who never experience symptoms despite being infected
Incubatory carriers
those who can transmit the agent during the incubation period before clinical illness begins
Convalescent carriers
are those who have recovered from their illness but remain capable of transmitting to others
Chronic carriers
who continue to harbor a pathogen such as hepatitis B virus or Salmonella Typhi, the causative agent of typhoid fever, for months or even years after their initial infection
why are carriers more likely to transmit than symptomatic
they do not realize they are infected, and consequently take no special precautions to prevent transmission.
Humans are also subject to diseases that have animal reservoirs
Many of these diseases are transmitted from animal to animal, with humans as incidental hosts
zoonosis
infectious disease that is transmissible under natural conditions from vertebrate animals to humans
Portal of exit
Portal of exit is the path by which a pathogen leaves its host
Modes of transmission
Direct
Direct contact
Droplet spread
Indirect
Airborne
Vehicleborne. infectious agent include food, water, biologic products (blood),
Vectorborne (mechanical or biologic)
what happen in direct transmition
In direct transmission, an infectious agent is transferred from a reservoir to a susceptible host by direct contact or droplet spread.
Portal of entry
The portal of entry refers to the manner in which a pathogen enters a susceptible host. The portal of entry must provide access to tissues in which the pathogen can multiply or a toxin can act
Susceptibility of a host depends on
genetic or constitutional factors, specific immunity, and nonspecific factors that affect an individual’s ability to resist infection or to limit pathogenicity. An individual’s genetic makeup may either increase or decrease susceptibility
examples Nonspecific factors
include the skin, mucous membranes, gastric acidity, cilia in the respiratory tract, the cough reflex
what can increase risk
disrupting host defenses include malnutrition, alcoholism, and disease or therapy that impairs the nonspecific immune response
Knowledge of the portals of exit and entry and modes of transmission provides
a basis for determining appropriate control measures.
Interventions are directed at:
Controlling or eliminating agent at source of transmission
Protecting portals of entry
Increasing host’s defenses
mode of transmission. Interruption of direct transmission may be accomplished by isolation of someone with infection
For airborne diseases prevention
strategies may be directed at modifying ventilation or air pressure, and filtering or treating the air
To interrupt vectorborne transmission
measures may be directed toward controlling the vector population, such as spraying to reduce the mosquito population.
The concept of herd immunity suggests
if a high enough proportion of individuals in a population are resistant to an agent, then those few who are susceptible will be protected by the resistant majority, since the pathogen will be unlikely to “find” those few susceptible individuals. 85% to 90%
One problem is that
in highly immunized populations, the relatively few susceptible persons are often clustered in subgroups defined by socioeconomic or cultural factors. If the pathogen is introduced into one of these subgroups, an outbreak may occur.
HAIs
infections that patients get while receiving treatment for medical or surgical conditions,
Risk factors for HAIs can be grouped into three general categories
medical procedures and antibiotic use, organizational factors, and patient characteristics.5
The behaviors of health care providers and their interactions with the health care system also influence the rate of HAIs.
preventing HAI
proper education and training of health care workers adoption of best practices ( infection control, hand hygiene, attention to safety culture, and antibiotic stewardship)
Examples of best practices by a health care provider include careful insertion, maintenance, and prompt removal of catheters, careful use of antibiotics.
decolonization of patients with an evidence-based method to reduce transmission of MRSA in hospitals.7
