Hawker 3rd edition Flashcards
What are the components of the epidemiological triangle
The agent, a susceptible host, and environmental factors
Example of agents
.Virus
.Bacteria
.Fungus
.Parasites
Name some examples of Host factors
age, sex, socioeconomic status, ethnicity, lifestyle factors, genetic makeup, etc.
All these factors influence host probability/ lvl of exposure, susceptibility and response to the agent
Name some example of environmental factors
Geology climate physical surroundings biological factors (population of insect vectors in an area) Socioeconomic factors
Define endemic
“A persistent low or moderate level of disease”
Define hyper-endemic
” A higher persistent level of disease”
Define sporadic
“An irregular pattern with occasional cases occurring at irregular intervals”
Define Epidemic
“When the occurrence of an infection exceeds the predicted lvl for a given time period” the word outbreak is also used for this
Define pandemic
” When epidemic spreads over a wide geographic area”
What does an epidemic curve show?
a frequency histogram of number of cases against time or date of onset
What is a point source outbreak
Exposure to an infectious agent taking place over a relatively brief period.
What does the epidemic curve for a point source outbreak look like?
http://www.med.uottawa.ca/sim/data/public_health_epidemic_curves_e.htm
What is a propagated outbreak
An outbreak that spreads from person to person
What does the curve for a propagated outbreak look like ?
http://www.med.uottawa.ca/sim/data/public_health_epidemic_curves_e.htm
Why does an epidemic wane after a few generations
The number of people susceptible falls below a critical lvl
What is a mix epidemic?
An epidemic in which the epidemic curve shows both common source and propagated epidemic features due to secondary person-person spread
What two rates are used to describe the occurrence of infection diseases
Prevalence= existing cases at a given point in time/ persons at risk Incidence= New cases over a given time period/ persons at risk
What is the pathway for the chain of infection
Agent leaves the reservoir or host through a portal of exit and is conveyed by a more of transmission. It enters a susceptible host via a portal of entrance
What is a reservoir and describe some example
A location in which the agent normally lives and multiplies. This can be a person, animal, arthropod, plant , soil, a substance or a combination of these things. Note this can be different from source or vehicle of infection.
What is the source/ vehicle of infection
The mode of transport used by an infectious agent to pass to a host
What colonisation in relation to infection
The presence of a micro-organism in or on a host, with growth and multiplication BUT without sign of infection
What are zoonses
Infectious agents which are transmissible from animals to humans
What is the portal of exit
The path used by the infectious agent to leave the host. This tends to be an area where the agent is localised for example the respiratory tract
What is the portal of entry
The route used by the infectious agent to enter a susceptible host
What is the mode of transmission
The mechanism by which a infectious agent is spread from a source/ reservoir to a susceptible person.
What is the natural progress of a disease
The progression of a disease in an individual without intervention
What is the incubation period
A period of time in which the infectious agent is present within the host, but does not cause any pathological changes or such changes are subclinical. This period ends with the onset of disease . For any given disease the incubation period has a range and mean value
When does a screening program attempt to detect a disease
The incubation period or the early phases of its natural history
When are diagnoses made
On the onset of symptoms, where changes have moved from subclinical to clinical. In some people the disease never spreads to a clinically apparent illness. If they do manfest they can range from mild to fatal
What is the infectious period
The time point in which an infectious agent may be transmitted directly and indirectly from an infected person to another person
When are disease are most infectious
Depends on the infectious agent. Some disease are more infectious during the incubation period than the onset of illness.
What are the 3 categories of transmission
.Direct transmission- this is via direct contact such as touching , kissing ect
.Indirect transmission- can be Vehicle-borne can involve fomites, food . The agent may or may not multiple on the vehicle before transmission. The other formis vector born such as being carried by an insect. This does not require multiplication or development of the agent
.Airborne spread- dissemination if a microbial aerosol to a suitable port of entry, normally the respiratory tract
Name some examples of direct transmission
Direct route- Infection via skin, mouth, eyes spread by touching and infected area or person
Respiratory route-sneezing, coughing, from an infected person close by
Faecal to oral- when faeces are transferred directly to the mouth of the susceptible host
Name examples of indirect transmission
Faecal-oral route- Contaminated food or objects like flush handles. Indirect animal vectors such as flies may transfer the faeces.
Bloodborne route. The transfer of blood or body fluids from an infected person to another person via a break in the skin, a bite wound etc
Respiratory route- droplets from mouth and nose may contaminate hands and fomites and thus contaminate those who touch them
Example of diseases which are air-borne
Legionella, coxiella
What standard precautions are used to prevent disease
.Handwashing
.Covering of wounds or skin lesions
.Use of protective equipment eg gloves
.Respiratory and cough hygiene and etiquette
.Prevention and management of needlestick injuries, injuries from sharp and blood splash incidents
.safe disposal of contaminated waste
. Managing spillage of blood and body fluids
.Decontaminating equipment including cleaning, disinfection and sterilisation
.Safe collection and transport of specimens
.Maintaining a clean clinical enviroment
.Safe management of used linen
.Place patients with infections in appropriate accommodation
What is the step process when dealing with a public health issue
.Define the problem .collect the necessary information .Undertake a risk assessment .Identifying good practice .implement the response .Evaluate the outcome
What two questions need to be asked when dealing with a communicable disease
1- where did the case get it from?
2- Is the case likely to pass it on?
What is meningitis
The inflammation of the meninges .
What is meningism
Meningism is the group of signs and symptoms that accompanies the inflammation. Note you can have meningitis without meningitis but meningitis is the most common cause.
What are the classic symptoms of meningism
Headaches
neck stiffness
nausea or vomiting
photophobia
What is the cause of meningitis caused by
Acute meningitis is nearly always caused by:
1-viral or bacterial
2 fungal and protozoal infection can occur but rely on immunosuppressed patients
What viruses can cause meningitis
Commonly caused by enterovirus infection eg echovirus or coxsackievirus. Viral meningitis is common but most cases are mild or inapparent
Rare viruses that can cause meningitus
.Poliovirus .Mumps virus .Influenza type A or B .Rubella .Epstein-barr virus
Bacterial meningitis is caused by
.E.coli- particularly emergency in infants
group B- streptococci - again common in infants
.Meningococcal meningitis- common in older infants and younger children. Caused by Neisseria meningitidis
.Haemophilus influenzae- occasionally occurs in unvaccinated children and adults. Has a slower onset than meningococcal
What is a common sign of meningococcal Meningitis
A haemorrhagic rash
What bacteria causes meningococcal DISEASES
Neisseria Meningitidis
What are the two Meningococcal DISEASES
Meningitis- inflammation of the meninges
Septicaemia- a systemic infection with widespread signs, and generalised organ damage
What is the reservoir for Neisseria Meningitidis
Humans are the only reservoir
Why is Neisseria Meningitidis such a problem
the incubation period is short and therefore kills a person quick
Meningococcal meningitis symptoms
Headaches neck stiffness nausea or vomiting photophobia fever
What are the symptoms of meningococcal septicaemia
Cold hands and feet Circulatory collapse Pale, blotchy or mottled skin Muscle or joint pains Petechial, non-blanching rash (doesn't disappear when pressed), becoming purpuric (purplish discolouration of the skin)
Why does meningococcal septicaemia cause these symptoms
As side effect of the immune system attacking the disease. The proteases used to break down the bacteria also can break down the capillarity lining
What laboratory test can we use for bacterial meningitis
A gram stain. Due to the bacteria being gram negative, the stain will show their presence. The only exception is when TB causes meningitis
What common investigation tests are used for bacterial meningitis
Blood culture- this may show negative result if the patient has received antibiotics before admission •Lumbar puncture- this may show negative result if the patient has received antibiotics before admission. Clinicians are reluctant to conduct a lumbar •Throat swab •Rash aspirate •PCR for N meningitidis •Serology •Full blood count •CRP (inflammatory marker)
What are the diagnostic methods for meningitis
Gold standard is culture of the germ from a normally sterile site: e.g. cerebrospinal fluid, blood, joint fluid
•Culture from throat swab, rash aspirate
•Direct microscopy: Gram negative diplococci
•PCR for N meningitidis
•Antigen detection (especially for Group C)
•Serology (retrospective)
When should you notify about a possible outbreak for meningitis?
Notify on suspicion – don’t wait for laboratory confirmation as public health action needed ASAP, better to be safe than sorry according to Edward
What are the three types of cases in the development of an outbreak
Confirmed case: clinical diagnosis with lab confirmation (immediate PH action)
Probable case: clinical case with no lab confirmation, but meningococcal disease is most likely (immediate PH action)
Possible case: no lab confirmation and other diagnosis is equally likely (no immediate PH action)
What is the most common type of Neisseria Meningitidis in europe and what is the common type in asia and africa
Europe and americas- B and C
Asia, africa- A
What preventative and control measures can we take for hygiene for meningitis
General measures such as hand washing, particularly in hospitals. Enteroviral meningitis usually spreads as a result environmental contamination
How can we reduce the chance of pregnant women passing on bacterial meningitis
Intrapartum antibiotic treatment for colonised women. Useful for Group B streptococcal meningitis
What is a population approach we can take to reduce lvls of meningitis
Immunisation in childhood especially MMR vaccine
what type of vaccine is given in the uk and who to (for meningitis) ?
Meningitis type C. It is given to those under 18 and to students starting university and those under 25
Why is group B vaccine for meningitis not given?
Biologically difficult to produce.
•Antigenically similar to brain protein.
•In UK, multiple strains of serogroup B, so not easy to produce a “one size fits all” vaccine.
•Group B vaccine developed, currently given routinely for infants from 1 September 2015, but ongoing issues with uncertainty of effectiveness and high costs
What is the purpose of Chemoprophylaxis
This is given to close contacts of a case, meningococcal and Hib disease. It is a type of antibiotic which is designed to clear out the throat carriage where the bacteria reside. This therefore prevents further spreading of the bacteria. It is not appropriate viral pneumococcal meningitis
What food safety measures for meningitis
For listeria meningitis is preventable by avoiding high risk foods such as:
.soft cheese
pate
cook-chill foods
This is important for immunosuppressed and those pregnant
Where are the common clusters for meningitis
Most common in teenagers/youths
•Outbreaks occur in schools/colleges
What does the action plan depend on for meningitis
Attack rate
•Isolation of the same organism
•Establishing a link between cases
•Public anxiety
How do you investigate cluster links in the community for meningitis
Look for links
•Define an at risk population
•Calculate age-specific attack rates
•No specific threshold, but look for a substantial increase
How do you respond to a case or cluster of meningitis(more indeepth)
.1st priority is establishing a diagnosis by working with microbiologists and clinicians
.2nd if it is viral meningitis then no further steps are needed at this stage but it may be necessary to provide information to GP’s if the case appears to be linked
. In the event of a bacterial case; 1 further investigation is needed to determine the bacteria causing the disease
.Establish if cases are linked
.Apply chemophylaxis and vaccination program when necessary
How do we define a GI infection
Any infection from whatever source, of the GI tract. Tends to result in common symptoms such as vomiting and diarrhoea.
How many people in the uk attend their GP with acute gastroenteritis ?
1 in 30 but many more suffer without attending their GP
What are the common causes of GI inefections
.bacteria
.viruses
.parasites
.In some cases chemicals or toxins (from things such as shellfish and fungi)
What are the common Gi infections
.Amoebic .bacillary dysentery .cholera .typhoid .paratyphoid fevers .noravirus .Campylobacteriosis .E.coli
What is Gastroenteritis
Acute diarrhoea and/or vomiting caused by a microorganism or toxin, directly acting on the GI tract. This results in inflammation of the bowel which produces these symptoms
What property of diarrhoea is important to observe?
Consistency of stool is more important than frequency
What is food poisoning
An illness which occurs after the ingestion of food. It is commonly but not always gastrointestinal
What two pathogens are not considered causes of food poisoning despite being spread through ingestion
.Typhoid.
.Hepatitis A
.Brucellosis
What does a short incubation period result in?
Most likely vomiting as the agent has not has much time to move down into the GI tract
How long is the average incubation period for staphylococcus aureus
2-4 hrs
How is staphylococcus aureus transmitted
It normally come from a food handler will have an infection. It can be spread via a wound, a boil or even asymptomatic staphylococcus in the nose or skin
How does staphylococcus aureus cause infection
- Staphylococcus lands on food after its been cooked
- under the right condition it grows and forms a toxin
- note only certain types of staphylococcus produce enterotoxin
- Staphylococcus can not survive boiling or freezing but the toxin does
- The ingested toxin causes vomiting
- It has a short incubation period
What foods do staphylococcus prefer
- slightly sugary or salty food
- Foods which have been left at room temperature either before or after cooking
What is the difference between Bacillus cereus (emetic type ) and Staphylococcus
It is naturally found in food unlike Staphylococcus, especially things such as rice
What is the pathway for bacillus cereus to cause disease
- in warm moist conditions bacillus cereus will grow and produce toxins
- The bacillus is not destroyed completely by boiling as it develops spores
- For example if boiled rice is let to cool slowly, the spore will become vegatated and produce toxin which will emetic
How do you diagnose bacillus cereus poisoning
cannot be made solely by identifying the microorganism as it may no longer being in the food. The best method is finding the type of toxin and establishing if it is high concentration. It must be found in the food and in the vomit or stool
How do you diagnose staphylococcal poisoning
cannot be made solely by identifying the microorganism as it may no longer being in the food. The best method is finding the type of toxin and establishing if it is high concentration. It must be found in the food and in the vomit or stool
Name two causes of gastroenteritis which have a short incubation period and are not microorganisms
- raw red kidney beans
- Heavy metals
How long is bacillus cereus incubation period
1-6 hrs
Describe Salmonellas
- Salmonellas are an extensive species of organisms that are probably the most common cause of food poisoning
- It can infect animals, birds and humans
- It requires a high dose to cause symptoms
What are the three ways salmonellas contamination can occur
1-method infection of poultry or animals from feed. This consumption of infected animal produce results in infection. This occurred with infected chicken eggs
2- Salmonella can spread directly to food or water through fecal contact
3- cross contamination may occurs from one food from another in the kitchen
What is clostridium perfingens
is a Gram-positive, rod-shaped, anaerobic, spore-forming pathogenic bacterium of the genus Clostridium.C. perfringens is ever present in nature and can be found as a normal component of decaying vegetation, marine sediment, the intestinal tract of humans and other vertebrates, insects, and soil.
What is the pathway for infection for clostridium perfringens
- The bacterial spore get onto food contaminating them
- In the scenario of inadequate reheating or if meat is cooked in bulk,
- The spores of clostridium perfringens germinate during the cooling process and multiply further especially if left for a long time in warmth
- Once ingested a toxin is formed from multiplying bacteria in the intestine
- Causing colic and diarrhoea
How can you diagnose clostridium perfingens
Finding the organism in food or stool is not enough. What is needed is finding high numbers of clostridium perfringens
enterotoxins are also available as a suitable method of diagnosis
What is the incubation period of clostridium perfingens
8-24 hrs
What is Clostridium botulinum
a Gram-positive, rod-shaped, anaerobic, spore-forming, motile bacterium with the ability to produce the neurotoxin botulinum
What does Clostridium botulinum do to the body?
Prevents the release of acetylcholine causing muscle to be in a state of paralysis
What three types of botulinum affect humans
A
B
E-found in fish
Symptoms include?
Nausea, vomiting or diarrhoea followed by symmetrical paralysis of the cranial nerves leading to blurred vision and difficulty in swallowing and speaking
What is Shignella
a genus of Gram-negative, facultative anaerobic, nonspore-forming, non-motile, rod-shaped bacteria , that is the cause of human shigellosis. It is one the world’s leading cause of diarrhoea
What is shigellosis
A disease caused by the gram-negative bacteria shignella which leads to dysentry
What is the pathway shignella takes to cause disease
It invades the distal part of the small intestine and the colon and causes acute watery, mucoid or bloody diarrhoea . Fever and intestinal colic also commonly occur
How is diagnosis of shigellosis made
Isolation of the organism from stool samples and serogrouping to identify the strain
How does shignella spread
Unlike simonellas, it does not survive well in food although some cases have occured from lettuce.
What is E.coli
is a Gram-negative, facultatively anaerobic, rod-shaped, coliform bacterium of the genus Escherichia that is commonly found in the lower intestine of warm-blooded organisms.Most E. coli strains are harmless, and some strains make up the normal flora of the gut and have a symbiotic relationship with the host.
what are the three methods e.coli cause disease
.-enteropathogenic
- enterohaemogenic
- enteroinvasive
what is E.coli 0157 method of transport into a human
- Found naturally in a cows stomach but does not cause disease
- When the cow is slaughtered, if the meat comes into contact with feces or stomach contents it can become infected
- person eats uncooked meat
- you can also get it from contaminated raw milk, contaminated water
- essentially ingesting anything contaminated
What are the high risk setting for E.coli 0157
. Nurseries
.Restaurants
.Petting farms
.ECT
What are the particular at risk groups for E.coli 0157
. children under 5
.older people
What can not be done to reduce GI infections
Vaccinations- many GI pathogens do not have vaccines
What can governments do to prevent GI infections
Implement a stick food and safety procedures to retailers. This is an issue within developing countries
What is HACCP
Hazard Analysis Critical Control Point. This is a system used in the food industry in identifying and assessing hazards in food and establishing control measures needed to maintain a cost-effective food saftey programme
What are the measures local authority can take to prevent GI infection
- Reinforce food saftey standards via health inspections
- excluded cases/carries of infection from work/school and compensate them
- seizure of food and closure of premises that present an imminent risk
- Educate the public on food handling (can be nationally implemnted as well)
- Encourage hand washing after eating or going to the toilet
- Adequate infection control policies in school, hospitals, nursing home, ect
What important epi data should be reported for GI infections
-Surveillance to detect outbreaks
-Food poisoning cases even is they are suspected
-Water born infections
-Levels of dysentery
- levels of viral hepatitis, cholera, typhoid
This is all done is the better to be safe than sorry principle
When issues occurs with a GI infection individual cases
It is not usually possible to identify the organism causing gastroenteritis on clinical grounds in individual cases
What steps should be taken when dealing with an individual gastroenteritis cases
- limit secondary spread from identified cases via provisions of general hygiene advice to all and by specific exclusion from work/school/nursery of those at risk of transmitting the infection
- Collect dataset to compare this case with other cases and identify any common exposures and potential outbreaks. ( used a standardised procedure to do this)
- Collect faecal samples from the cases of food poisoning or dysentery. Important in identifying if a serious pathogen is involved
- Set up a local team that includes local environmental health officers, microbiologists and clinicians
- request GP’s report any information similar to this case
What should be the response to gastroenteritis clusters
- Discover the microbiological agent using stool samples from the most recent patients and identify all relevant organisms. The agent will determine the urgency of the investigation to prevent further exposure to a source.
- Control measures to be introduced
- In the time needed for clinical results to arrive, details should be collected from all reported cases in order to build a profile on symptoms, incubation period, severity and duration of illness. These can be compared to case histories for similarities
- conduct on environmental investigation
When conducting an environmental investigation for a GI infection
1- food sources, storage, food prep and cooking procedures, temperature control after cooking and reheating
2-Symptoms of gastrointestinal or skin disease or testing for faecal carriage in food handlers
3- General state of knowledge of the staff and condition of the premises
4-examination of records of key controls such as pest control and temperature
5-Whether samples of food are available for examination/analysis and whether environmental swabbing or water sampling is appropriate
What is characteristic about influenza?
- upper and lower respiratory tract infection
- malaise ( a general feeling of uncomfort)
- Fever
- Aches and pains
- occasionally a dry cough
What are the three genera of influenza
- A
- B
- C
Out of the three genera, what is the scale of seriousness ?
Influenza A is the most serious. This causes major pandemics and is associated it pneumonia. Type B can cause severe outbreaks (compared to type C), and mainly impacts school children. Type C causes mild sporadic cases and rarely results in an outbreak
What is the method of transmission for influenze
- respiratory secretions- air droplets and small particle aerosols
- indirect: i.e in direct contact with contaminated surfaces . This may cause a slowly evolving outbreak with a low attack rate
What facilitates influenza transmission
- overcrowding
- in closed spaces (especially with people who are susceptible)
What is the natural reservoir for influenza
it is zoonotic particularly waterfowl. Transmission directly from waterfowl is rare but new strains can spread directly or through an intermediary such as a pig
What type of influenza only infects humans
type B
The two proteins Haemagglutinin(H) and Neuraminidase(N) are used to class influenza subtypes. What are they?
Both Haemagglutinin and Neuraminidase are surface proteins found on the surface of the virus. Haemagglutinin acts hook which binds the virus to cells while neuraminidase is an enzyme which allows new viruses to escape from the host cell.
Why is Influenza A so difficult to deal with?
Has a lot of genetic mutations
Why is seasonal flu a thing
Due to antigenic drift causing the virus to change a bit every year
When does seasonal flu occur
Occurs most often in the winter months and usually peaks between December and March in the northern hemisphere. Flu like symptoms can appear in summer but this is most likely due to another virus. In topical conditions there is sometimes nothing like seasonal flu
What is antigenic shift
Gene re-assortment & major antigenic variation, this can result in pandemics
How do we diagnose influenza
Take swabs from Nasopharyngeal aspirates, nasal swabs or throat swab.
carry out immunofluorescence to allow isolation of virus, then conduct either rapid antigen testing, PCR or serology
