Epidemiological Considerations Flashcards
What is the definition of epidemiology?
The study of the distribution and determinants of health-related states or events in specified populations and the application of this study to control of health problems
Tracking a disease within a population
What is the definition of infection?
Presence of an infectious organism in an individual or population?
What is the definition of disease?
Detectable clinical consequence of infection
What is the definition of incubation time?
Time interval between exposure to infection and appearance of disease
What is the definition of infectious?
Infected person capable of transmitting infection to others (not everyone who carries a pathogen is infectious)
What is more difficult to control: a disease with a long or short incubation time?
Diseases with long incubation times are harder to control because someone who doesn’t know that they are infected may still be able to spread the disease before the onset of symptoms
What is the definition of transmission?
The spread of infection
What is the definition of symptoms?
What the patient feels (pain, malaise)
This is subjective and can change (cannot be measured)
What is the definition of signs (e.g., signs and symptoms)?
Objective and concrete (can be measured through direct observation)
What is the definition of communicable?
It the spread of a microbial disease from one individual to another, either direct or indirect
Examples of communicable diseases are gonorrhoea, chickenpox, measles, mumps
What is the definition of contagious?
Microbial diseases that easily spread
It is a subcategory of communicable diseases
Example: chickenpox, measles
What is the definition of non-communicable?
Microbial diseases that cannot spread through individuals
Example: tetanus
Describe the time periods of infection
A susceptible host gets infected. There is a latent period when they are not infectious (generally for short time) because the pathogen is multiplying. Once the organism has multiplied to a high enough concentration, then there is the infectious period. Then the pathogen will leave the host and the host is no longer susceptible
Descriebt he time periods of infectious diseases
The susceptible host gets infected and there is an incubation period (no signs or symptoms). When symptoms appear, this is the disease period. The latent period of infection is generally shorter than the incubation period of disease
What is an endemic disease?
A disease that exists in a population (this is important for traveling). These diseases exist all the time in at low numbers
What is a sporadic disease?
The disease generally does not exist in a certain location but there may be a spike occasionally
What is an epidemic?
An outbreak in a larger geographical area
What is a pandemic?
An epidemic that spreads across continents
What is an acute microbial disease?
A rapidly developing disease with a short duration (e.g., influenza)
What is a chronic microbial disease?
A disease that usually develops from chronic infections
They are slow to develop with continual duration (e.g., tuberculosis)
What is a latent microbial disease?
A ‘silent’ disease
It is inactivated for certain periods of time (e.g., chickenpox/shingles)
What is a cross-sectional study?
Cross-sectional studies measure the frequency of an out- come and/or exposure(s) in a defined population at a par- ticular point in time
What type of questions do cross sectional studies answer?
What proportion of the population has evidence of a past infection with Lyme disease?
Is hepatitis B associated with hepatocellular carcinoma?
What is a case-control study?
Case–control studies identify people with the outcome (cases) and a representative group of people without the out- come (controls). Cases and controls are then compared with regards to differences in their past exposure
What types of questions do case-control studies answer?
Does exposure A cause disease B?
Are women with cervical cancer more likely to be infected with human papillomavirus than women without cervical cancer?
•Is injecting drug use associated with hepatitis C?
What is a cohort study?
Cohort studies follow a group of people who do not ini- tially have the outcome of interest and determine whether they develop the disease (descriptive cohort study)
What types of questions do cohort studies answer?
How high is the mortality among patients with methicillin-resistant Staphylococcus aureus septicaemia?
Does infection with human herpesvirus-8 cause Kaposi sarcoma in HIV-infected individuals?
What is an intervention study?
In an intervention study, disease-free and exposure-free individuals are actively allocated an exposure (interven- tion) or no exposure (no intervention). The two groups are then followed over a period of time and the frequency of the outcome is compared between the two groups
What is a randomized intervention study?
Randomized–controlled studies are a subtype of intervention studies and are considered the ‘gold stan- dard’ type of study because, when rigorously designed and conducted, they provide very strong evidence of causal associations. The intervention is allocated at random which means that every participant has the same chance of receiv- ing the intervention
What types of questions do intervention studies answer?
Is a new vaccine effective in preventing pneumococcal disease in children?
Do steroids improve the outcome in children with meningococcal disease?
How can we characterize outbreaks?
They can be local or widespread
