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http://www.iaff.org/hs/resi/infdis/What_are_the_modes_of_transmission.htm
THE CHAIN OF INFECTION
What are the modes of
transmission?
Exposure occurs through either direct or indirect contact.
Direct transmission occurs when a pathogen is transmitted directly from an infected
individual to you. For example, you could become infected with HBV if you had an open
wound that came into contact with a patient’s HBV infected blood.
Indirect transmission occurs when an inanimate object serves as a temporary reservoir
for the infectious agent. For example, you could become infected with HBV if you come into
contact with equipment that has dried infectious blood on it.
It is important to note that many diseases do not manifest themselves
immediately. Therefore, it can often be difficult to track the source of an exposure.
Many of the symptoms of some diseases can be quite similar to the flu. Therefore, if flu-like
symptoms do not subside in a normal amount of time with normal treatment methods, you
may need to have blood tests performed to rule out other possible causes.
http://science.education.nih.gov/supplements/nih1/diseases/guide/understanding1
.htm
Modes of transmission
Infectious agents may be transmitted through either direct or indirect contact. Direct contact occurs when an
individual is infected by contact with the reservoir, for example, by touching an infected person, ingesting infected
meat, or being bitten by an infected animal or insect. Transmission by direct contact also includes inhaling the
infectious agent in droplets emitted by sneezing or coughing and contracting the infectious agent through intimate
sexual contact. Some diseases that are transmitted primarily by direct contact with the reservoir include ringworm,
AIDS, trichinosis, influenza, rabies, and malaria.
Indirect contact occurs when a pathogen can withstand the environment outside its host for a long period of time
before infecting another individual. Inanimate objects that are contaminated by direct contact with the reservoir (for
example, a tissue used to wipe the nose of an individual who has a cold or a toy that has been handled by a sick
child) may be the indirect contact for a susceptible individual. Ingesting food and beverages contaminated by contact
with a disease reservoir is another example of disease transmission by indirect contact. The fecal-oral route of
transmission, in which sewage-contaminated water is used for drinking, washing, or preparing foods, is a significant
form of indirect transmission, especially for gastrointestinal diseases such as cholera, rotavirus infection,
cryptosporidiosis, and giardiasis.
These modes of transmission are all examples of horizontal transmission because the infectious agent is passed
from person to person in a group. Some diseases also are transmitted vertically; that is, they are transmitted from
parent to child during the processes of reproduction (through sperm or egg cells), fetal development, or birth.
Diseases in which vertical transmission occurs include AIDS and herpes encephalitis (which occurs when an infant
contracts the herpes simplex type II virus during vaginal birth).
Chain of infection for foodborne disease:
Essentials of food sanitation
http://www.ovc.uoguelph.ca/personal/ecosys/documents/Lecture1-IntrotoFBD.pdf
Chain of Infection
There are a number of ways to gauge validity of findings or conclusions. Because there are 9 items in
the Bradford Hill model, I think they might mean that:
(from http://www.epidemiolog.net/evolving/CausalInference.pdf but I like the Wikipedia
explanation: http://en.wikipedia.org/wiki/Epidemiology
The Bradford Hill criteria
1. Strength of the association – The stronger an association,
the less it could merely reflect the
influence of some other etiologic factor(s). This criterion
includes consideration of the statistical
precision (minimal influence of chance) and methodologic
rigor of the existing studies with
respect to bias (selection, information, and confounding).
2. Consistency – replication of the findings by different
investigators, at different times, in different
places, with different methods and the ability to convincingly
explain different results.
3. Specificity of the association – There is an inherent
relationship between specificity and strength
in the sense that the more accurately defined the disease
and exposure, the stronger the observed
relationship should be. But the fact that one agent
contributes to multiple diseases is not
evidence against its role in any one disease.
4. Temporality – the ability to establish that the putative
cause in fact preceded in time the
presumed effect.
5. Biological gradient – incremental change in disease rates
in conjunction with corresponding
changes in exposure. The verification of a dose-response
relationship consistent with the
hypothesized conceptual model.
6. Plausibility – we are much readier to accept the case for a
relationship that is consistent with our
general knowledge and beliefs. Obviously this tendency has
pitfalls, but commonsense often
serves us.
7. Coherence – how well do all the observations fit with the
hypothesized model to form a
coherent picture?
8. Experiment – the demonstration that under controlled
conditions changing the exposure causes
a change in the outcome is of great value, some would say
indispensable, for inferring causality.
9. Analogy – we are readier to accept arguments that
resemble others we accept
Guess they want you to understand this model:
http://www.cdc.gov/excite/classroom/outbreak/steps.htm
for two ways, they wanted:
Step 10: Communicate Findings
Your final task in an investigation is to communicate your findings to others who need to
know. This communication usually takes two forms: 1) an oral briefing for local health
authorities and 2) a written report.
Your oral briefing should be attended by the local health authorities and people responsible
for implementing control and prevention measures. This presentation is an opportunity for
you to describe what you did, what you found, and what you think should be done about it.
You should present your findings in scientifically objective fashion, and you should be able
to defend your conclusions and recommendations.
You should also provide a written report that follows the usual scientific format of
introduction, background, methods, results, discussion, and recommendations. By formally
presenting recommendations, the report provides a blueprint for action. It also serves as a
record of performance, a document for potential legal issues, and a reference if the health
department encounters a similar situation in the future. Finally, a report that finds its way
into the public health literature serves the broader purpose of contributing to the scientific
knowledge base of epidemiology and public health.
Back to Top
Back to How to Investigate an Outbreak
10 Steps:
http://www.cdc.gov/excite/classroom/outbreak/steps.htm
Does the Excite 10 steps match this (from
http://www.kdheks.gov/epi/download/kansas_foodborne_illness_manual.pdf
SECTION 3 – The Epidemiologic Investigation 31
Steps of an epidemiologic outbreak investigation 33
Step 1. Determine that an outbreak has occurred
34
Step 2. Contact and coordinate with key personnel 35
Step 3. Obtain clinical specimens and food samples for laboratory testing
Step 4. Implement control and prevention measures
Step 5. Define cases and conduct case finding
38
38
37
Line list 38
Case definition 40
Case finding 41
Step 6. Describe the outbreak by time, place, and person
42
Epidemic curves 42
Maps and pictures 44
Frequency tables 44
Step 7. Develop possible hypotheses 45
Step 8. Plan and conduct the epidemiologic study to test hypotheses 45
Questionnaire 46
Study design 46
Logistics 49
Step 9. Analyze the data collected and interpret results
49
Step 10. Report the findings of the outbreak investigation
Intentional contamination of food 51
Match Excites?
50