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107 Cards in this Set
- Front
- Back
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Define basic reproductive number
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The average number of secondary cases produced by one primary case in a wholly susceptible population
Measure of the intrinsic potential for an infectious agent to spread Other things being equal, the larger the value of R0 the more difficult the infection is to control Measure of the intrinsic potential for an infectious agent to spread Other things being equal, the larger the value of R0 the more difficult the infection is to control |
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Def Effective reproduction number
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R= R0 x proportion susceptible
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Give the R0 for:
a. Measles b. Pertussis c. Mumps d. Rubella e. Diphtheria f. Polio |
a. 15-17
b. 15-17 c. 10-12 d. 7-8 e. 5-6 f. 5-6 |
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Def Herd immunity
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Herd immunity refers to the proportion of a host population which is immune to an infection
Concept that the presence of immune individuals protects those who are not themselves immune |
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Def Elimination
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Reduction of transmission risk to near zero
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Def Eradication
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reduction of transmission risk to zero
Control = reduction of transmission risks to pre-defined levels |
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Def Control
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reduction of transmission risks to pre-defined levels
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Give equ for R0
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probability of effective contact
x number of contacts x duration of infectiousness |
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Def Public Health Surveillance
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the ongoing systematic collection, analysis, and interpretation of data on specific health events for use in the planning, implementation, and evaluation of public health programmes
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Name the statutory notifiable conditions
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Acute encephalitis
Acute poliomyelitis Anthrax Brucellosis Cholera Diphtheria Haemolytic uraemic syndrome Food poisoning Leprosy SARS Malaria Measles Mumps Enteric fever (Typhoid or Paratyphoid fever Plague Rabies Infectious bloody diarrhoea Rubella Invasive group A Streptococcal disease and Scarlet fever Yellow fever Smallpox Tetanus Tuberculosis Legionnaires’ disease Typhus fever Whooping cough Viral haemorrhagic fever Botulism Acute Meningitis (meningococcal, pneumococcal, Haemophilus influenzae, viral, other specified, unspecified) Meningococcal septicaemia (without meningitis) Acute Viral hepatitis (Hepatitis A, Hepatitis B, Hepatitis C, other), |
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What is the value of surveillance
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Inform vaccination strategies and vaccine formulation
Guide clinical management in face of evolving antimicrobial resistance Identify outbreaks and guide disease control interventions Guide allocation of resources Detect and respond to emerging infections |
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Role of public health england
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1. COMMUNICABLE DISEASE CONTROL & PREVENTION
Infectious disease surveillance Outbreak Management Public Health consequences of infectious disease Immunisation programme implementation and evaluation 2. ENVIRONMENTAL HAZARDS/INCIDENTS Health aspects of environmental incidents Multi-agency planning focussed on environmental hazards 3. HEALTH EMERGENCY PLANNING & RESPONSE Preparing and responding to major incidents and health threats |
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Questions for outbreak investigation
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Is it an outbreak? (verified diag? cases linked? above average?)
Serious disease? How infectious? How preventable? |
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8 Steps of an outbreak investigation
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Confirm outbreak and diagnosis
Define case Identify cases and obtain information Descriptive data collection and analysis Develop hypothesis Analytical studies to test hypothesis Special studies (cohort or case control) Communication, including outbreak report |
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Principles of managing an outbreak
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Control
Investigate Communicate |
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Presentation Meningitis
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- case fatality 5%
- fever, vomiting, drowsiness, headache, photophobia, neck stiffness - myalgia, joint pains, rash |
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Presentation Septicaemia
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case fatality 20%
rash and shock cold hands & feet. Inc RR, stomach/ joint/ muscle pain Drowsiness/ impaired conciousness |
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N. menigitidus
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specific to humans
lives back of throat, not saliva fragile organism 10% population prevalence highest in young adults (20- 30%) more frequent in smokers duration 1-2 years mostly harmless, generates immunity |
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Risk factors: meningococcal disease
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TRANSMISSION FACTORS
overcrowding social (respiratory) contact contact with smokers HOST SUSCEPTIBILITY mucosal damage: viral infection, low humidity lower immunity: age, influenza, genetic factors, lack of vaccination ORGANISM VIRULENCE capsule essential clonal complex CLOSE CONTACT WITH A CASE |
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Prophylactic treatment for contacts of N. menigitidus outbreak
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Rifampicin
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What ways can clinicians conduct health promotion as individuals?
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Significant events opportunity for intervention
Brief interventions e.g. to quit smoking, reduce alcohol intake, exercise more Offer to refer elsewhere e.g. NHS stop smoking services, weight-management programmes Treat risk factors e.g. hypertension Be aware of risk factors eg suicidal ideation in depression |
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What ways can clinicians conduct health promotion at a community level
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Physicians working in CCGs or local authorities
Interventions aimed at whole community e.g. mailout inviting older people for flu jab |
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What ways can clinicians conduct health promotion at a population level
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Giving expert advice to policy makers, media, researchers
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Levels of Disease Prevention
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PRIMARY PREVENTION
prevent the onset of disease (reduces the incidence of disease) SECONDARY PREVENTION early identification and treatment of disease sometimes refers to identifying and treating risk factors (acts on prevalence: cures or prevents progression of disease) TERTIARY PREVENTION rehabilitate people with established disease (aims to reduce the number and/or impact of complications) |
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Define life course approach
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A life course approach investigates the long term effects on chronic disease risk of physical and social hazards during gestation, childhood, adolescence, young adulthood and later adult life (and across generations).
It studies the biological, behavioural and psychosocial pathways that operate across the life course and influence the development of chronic diseases. |
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What early life factors are potentially associated to CHD?
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Birth size – reflecting intrauterine/genetic exposures
Breast feeding Post-natal growth Childhood nutrition Childhood socioeconomic position (SEP) Childhood smoking Childhood obesity |
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When should secondary prevention begin?
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Once risk factors are identified to prevent a CHD event
Following a CHD event to prevent further events |
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Effective secondary prevention
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IDENTIFY those at risk: through a register (QOF register) of patients with CHD; and via NHS Health Checks (for 40-74 year olds)1
ADVISE over lifestyle factors: smoking cessation, healthy diet, reduce alcohol, physical activity, weight control TREAT risk factors, e.g. prescribe statins to lower serum cholesterol, ACE inhibitors to control hypertension |
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What other services other than advice can improve lifestyle risk factors
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Weight management service
“Exercise on prescription”, or activity programme such as “Walking for Health” Smoking cessation service |
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When should tertiary prevention begin?
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Once a CHD event has happened, to avoid long term complications, and improve quality of life
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Eg of tertiary prevention
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Cardiac rehabilitation
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Def Prevention Paradox
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‘…a large number of people at small risk may give rise to a larger number of cases of disease than the small number of cases who are at high-risk’
but… ‘….a preventative measure which brings much benefit to the population offers little to each participating individual’ |
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Advantages of Population Strategy of prevention
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Radical; removes reason the disease is common
Potentially powerful impact at population level Cultural shift: the change becomes the social norm so potentially long-term impact Individuals with unidentified risks/problems gain |
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Disadvantages of Population Strategy of prevention
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Little benefit to the individual (prevention paradox), so low acceptability
Can be costly Does not address health inequalities Low benefit to risk ratio |
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Advantages of High-Risk Strategy of prevention
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Prevention is appropriate to the individual: high acceptability
Easily accommodated within the organisation and ethos of medical care Cost-effective use of medical resources Selectivity improves the benefit to risk ratio Opportunity to address inequalities |
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Disadvantages of High-Risk Strategy of prevention
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Prevention is medicalised – labelling of individuals
Success is only temporary Problems of feasibility and costs - screening The contribution to overall control of disease is small |
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Give an eg of population strategies
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Home visiting to new mothers and babies by health visitors including Edinburgh Postnatal Depression questionnaire
Traffic light system for labelling foods in supermarkets Ban on smoking in public places Awareness and information campaigns to increase physical activity and healthy eating, e.g. Change4Life |
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Examples of High-Risk Strategies
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C-card condom distribution scheme for under 25s in areas of deprivation
Follow-up of recently discharged psychiatric patients to reduce risk of suicide Smoking cessation interventions for pregnant women Counselling-based interventions aimed at reducing alcohol intake of heavy drinkers |
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What is the UK Healthy Child Programme
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The prevention and early intervention public health programme of universal services for children and families
Philosophy: Progressive universalism |
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What does the UK Healthy Child Programme include?
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Includes:
Health promotion Assessment of development Screening Immunisation Keeping children safe (SUDI, Injury prevention, Child protection) Assessment of child and family needs |
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What ID are screened for in pregnancy? How?
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Rubella susceptibility
Syphilis HIV Hepatitis B Single blood sample, taken at booking |
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What foetal abN are screened for in preg? How?
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1) Down Syndrome testing – ‘combined test’ (blood + nuchal thickness ultrasound + risk factor assessment) between 10-14 weeks of pregnancy
Gives probability of having a baby with DS In absence of screening ~1 in 660 births affected (2) Fetal Anomaly ultrasound – between 18-21 weeks of pregnancy to look for physical abnormalities |
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Is screening for haemoglobinopathies routine? Which ones?
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No, but should be offered to all mothers.
Sickle Cell disease, Thalassaemia and other haemoglobinopathies |
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What is the Newborn & Infant Physical Examination (NIPE) screening
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Within 72 hours and at 6-8 weeks
Heart Eyes Hips Testes Facies B/O |
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What does the NIPE screen for?
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Congenital heart disease
8/1000 births (~1%) Cataracts 200 children / yr in UK May be associated with other conditions e.g. Down’s syndrome Developmental dysplasia of the hip 1-2/1000 births, girls>boys Larger number have unstable hips Cryptorchidism Both testes should be in scrotum by 1y 1% are undescended by 1y 1 in 20 premature boys affected |
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What is the Newborn Hearing Screening Programme
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Hearing screening should take place before discharge from hospital or within 2 weeks of birth if delivered in community / at home
Allows diagnosis of moderate or profound hearing loss by 4 wks to enable early initiation of effective communication between parents and their child Prevalence of condition: 1-2/1,000 are born with a hearing loss in one or both ears |
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What does the Newborn Bloodspot programme screen for? When is it performed?
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Heel prick blood test at 5-8 days of age tested for:
Hypothyroidism (HT) Cystic Fibrosis (CF) Sickle Cell disease Phenylketonuria (PKU) Medium-chain acyl-CoA Dehydrogenase Deficiency (MCADD) |
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How do we act on the Newborn Bloodspot programme abN?
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Enables early initiation of:
replacement therapies (HT and CF) diet (PKU and CF) health advice (all) |
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Out of 40K Blood spots, how many cases of...... will be identified:
a. Sickle cell disease b. Sickle cell trait c. PKU d. CHT e. MCADD f. Cystic Fibrosis |
a. 6
b. 97 c. 3 d. 19 e. 4 f. 19 |
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What is the Healthy Child Programme? What ages?
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5-19 years
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What does the Health assessment at school entry involve?
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Health assessment at school entry (age 5). This includes?
Review of health and care needs Review of immunisation status Measure Height and Weight as part of the National Child Measurement programme Hearing screening Vision screening (not colour vision) No routine physical examination |
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What are the actions for:
a. Missed immunisations b. Failed hearing screen c. Failed vision screen / concern about colour vision d. Overweight or obese |
a. Refer to GP
b. Refer to audiologist c. Refer to optician/orthoptist d. Advice + signpost to services |
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What additional measures in the Healthy Child Programme have for children in care?
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Annual health checks for looked after children
Support in school for children with Special Educational Needs (SEN) or long term illness or disability |
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Is the National Childhood Measurement Programme (NCMP) a surveillance programme or screening programme?
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Surveillance
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What are the stats on childhood obesity from the NCMP?
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One in ten children aged 5 is obese
One in five children aged 11 are obese Risk of becoming overweight or obese gets worse during primary school Overall levels of obesity are plateauing |
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What are the inequalities regarding childhood obesity?
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1. deprivation
2. ethnicity 3. gender |
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What is the Chlamydia screening
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To detect infection with chlamydia trachomatis
Commonest STI in GUM clinics in England Can lead to pelvic inflammatory disease (women) or reduced fertility (men) Testing available for any person <25y who has been sexually active Testing encouraged annually or on change of partner Those <16y can be tested if Fraser competent Contacts of test +ve cases included regardless of age |
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What approach does the Health Child Programme take with teenagers aged 11-16?
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Progressive
Support &/or referral for missed immunisations, emotional health needs or concerns about weight Referral for YP using drugs, alcohol, smoking or at risk of serious behaviour problems / crime |
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Which children require planning for the transition to childhood?
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Are looked after
Have special educational needs Have long term conditions or disabilities |
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What approach does the Health Child Programme take with teenagers aged 11-16?
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Universal & Progressive
As for 11-16y olds. Also offers: Increasing likelihood of additional sexual health needs Teenage pregnancy Transition to adult services for those with additional needs |
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What reasons are there to carry out a test?
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1) Detection of a disease (rule in diagnosis)
2) Exclusion of a disease (rule out diagnosis) 3) Following a protocol 4) Screening - to ascertain which individuals in an apparently healthy population are likely to have the disease of interest. Individuals flagged up in this way will then usually be subjected to more rigorous investigations to have the diagnosis confirmed 5) Staging test - e.g. for cancer 6) Monitoring test - to track a patient's progress over time |
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Define gold standard test
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Provides a definitive diagnosis of a disease
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What does a positive gold standard test mean?
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The gold standard test is positive for a disease the patient has the disease.
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INSERT PHOTO 1.1 epi from flashcards
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a = True positives. The number of people with the disease that the diagnostic test has identified.
b = False positives. The number of people without the disease that the diagnostic test is positive for. c = False negatives. The number of people with the disease that the diagnostic test is negative for. d = True negatives. The number of people without the disease for whom the diagnostic test is negative. a + c = The total number of people with the disease (as identified by the gold standard). b+ d = The total number of people without the disease (as identified by the gold standard). n = a + b + c + d = The total number of people undergoing the test (the total study population). |
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How do you calculate prevalence in this population from this table?
INSERT PHOTO 1.1 epi from flashcards |
(a+c) / n
ie. total # with disease / = being tested |
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Def and give equ for sensitivity?
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The proportion of individuals with the disease who are correctly identified with the test.
Sn-N-OUT Sensitivity Negative rules OUT True Positives /# with the disease ie TP / TP+FN |
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How do you calculate sensitivity in this population from this table?
INSERT PHOTO 1.1 epi from flashcards |
a / (a+c)
ie TP/# with the disease |
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Def and give equ for specificity?
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The proportion of individuals without the disease who are correctly identified by the test.
Sp-P-IN SPecificity Positive rules IN True Negatives / Total # without disease ie TN / TN+FP |
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How do you calculate specificity in this population from this table?
INSERT PHOTO 1.1 epi from flashcardsb |
D / (b + d)
ie True Negatives / Total # without disease |
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Def and give equ for PPV?
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The proportion of people with a positive test result who have the disease.
True positives / # of people the test has identified as +ve |
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How do you calculate PPV in this population from this table?
INSERT PHOTO 1.1 epi from flashcards |
a / (a + b)
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Def and give equ for NPV?
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The proportion of individuals with a negative test result who do not have the disease.
True negatives / # the test identified as -ve |
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How do you calculate NPV in this population from this table?
INSERT PHOTO 1.1 epi from flashcards |
d / (c + d)
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What are of the graph for this diagnostic test = TP, TN, FP, FN?
INSERT PHOTO 1.2 epi from flashcards |
INSERT PHOTO 1.3 epi from flashcards
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What is the....... with screening tests?
a. ideal characteristic b. purpose c. problem |
a. High Sensitivity SnNOUT
b. To detect as many people as possible who definitely have the disease. Ensure that not many true cases are missed. Can be used to 'rule out' the diagnosis. c. Will also include people who do not have the disease (false positives). Further diagnostic testing will be needed to deal with the false positives. |
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What is the....... with diagnostic tests?
a. ideal characteristic b. purpose c. problem |
a. High Specificity SPPIN
b. To detect as many people as possible who definitely do not have the disease. Ensure that not many cases are misdiagnosed. Can be used to 'rule in' the diagnosis c. Will also exclude some people who do have the disease (false negatives). Prior screening tests may be needed to deal with a high number of false negatives. |
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Define Likelihood ratios
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LRs offer a way of evaluating a test result in the context of a particular patient.
The likelihood ratios use the sensitivity and specificity of a test to determine if a test usefully changes the probability that patient has a particular disease. |
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Give the equ for the LR of a positive test result
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LR + = sensitivity / 1 - specificity
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Give the equ for the LR of a negative test result
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LR - = 1 - sensitivity / specificity
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Calculate the...... for this test:
a. sens b. spec c. ppv d. npv e. prevalence f. +ve LR INSERT PHOTO 1.4 epi from flashcards |
a. Sens = 0.938
b. Spec = 0.936 c. PPV = 0.625 d. NPV = 0.992 e. Prev = 10.1% f. +LR = 14.6 |
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How do you interpret these results?
a. Sens = 0.938 b. Spec = 0.936 c. PPV = 0.625 d. NPV = 0.992 e. Prev = 10.1% f. +LR = 14.6 |
a. SENS: the test correctly identified the disease in 93.8% of the cases
b. SPEC: the test correctly identified 93.6% of the patients without the disease c. PPV: 62.5% of the +ve results were true positives d. NPV: 99.2% of the -ve results were true negatives e. PREV: 10.1% of the cohort have the disease f. +LR: A +ve test is 14.6 time more likely to be found in someone with the disease than without the disease. |
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Which of the following are dependent on the prevalence of the disease of interest:
a) Sensitivity b) Specificity c) PPV d) NPV e) Likelihood ratio |
a. No - Sensitivity is the proportion of individuals with the disease correctly identified. It is therefore independent of disease prevalence.
b. No - Specificity is the proportion of individuals correctly identified as not having the disease. It is therefore independent of disease prevalence. c. Yes - the higher the disease prevalence the higher the PPV d. Yes - the higher the disease prevalence the lower the NPV e. No - the likelihood ratio depends on the sensitivity and specificity of a test. Neither of which depend on the prevalence of the disease |
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Insert Photo epi 1.6
How does increasing the threshold of a diagnostic test impact: a. Specificity b. Sensitvity c. PPV d. NPV |
Insert Photo epi 1.5
a. decrease sensitivity b. Increase specificity c. increase PPV d. decrease NPV |
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Insert Photo epi 1.7
How does decreasing the threshold of a diagnostic test impact: a. Specificity b. Sensitvity c. PPV d. NPV |
Insert Photo epi 1.8
a. increase sens b. decrease spec c. decrease PPV d. increase NPV |
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How do you calculate lower bound 95% confidence intervals?
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mean - (1.96) X SD / √n
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How do you calculate upper bound 95% confidence intervals?
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mean + (1.96) X SD / √n
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Is a big or small confidence interval better?
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Small.
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When does the 1.96 change?
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If sample size < 30 then uses 2.26
If sample size is >30 use 2.0 If sample size is very large use 1.96 |
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Define Pretest Probability
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The probability of the target disorder before a diagnostic test result is known.
It represents the probability that a specific patient, say a middle-aged man, with a specific past history, say hypertension and cigarette smoking, who presents to a specific clinical setting, like Accident and Emergency, with a specific symptom complex, say retrosternal chest pressure, dyspnoea and diaphoresis, has a specific diagnosis, such as acute myocardial infarction. |
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What are the uses of pre-test probability?
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1. interpreting the results of a diagnostic test,
2. selecting one or more diagnostic tests 3. choosing whether to start therapy: . a) without further testing (treatment threshold); . b) while awaiting further testing; 4. deciding whether it's worth testing at all (test threshold) |
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Give 3 ways to calculate pre-test & post-test probabilities
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1. from predictive values
2. likelihood ratios 3. Relative risk |
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Give equ for pre-test & post-test probabilities from predictive values
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Pre-test = (TP + FN) / Total = Prevelance
+ve test result --> +ve Post-test = TP / (TP + FN) = PPV -ve test result --> -ve Post-test = TN / (TN + FP) = NPV |
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Regarding pre-test & post-test probabilities? What does a LR > 1 produce?
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A LR greater than 1 produces a post-test probability which is higher than the pre-test probability.
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Regarding pre-test & post-test probabilities?
What does a LR < 1 produce? |
An LR less than 1 produces a post-test probability which is lower than the pre-test probability.
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Give the equ required to calculate +ve and -ve post-test probabilities using liklihood ratios
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Pretest probability = (TP + FN) / Total #
Pretest odds = (Pretest probability / (1 - Pretest probability) Likelihood ratio positive = sensitivity / (1 − specificity) Likelihood ratio negative = (1 − sensitivity) / specificity +ve Posttest odds = Pretest odds * +ve Likelihood ratio +ve Posttest probability = Posttest odds / (Posttest odds + 1) |
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What is the equ for pre-test odds?
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pre test odds / (pre test odds + 1)
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Give equ for post-test odds
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pre-test odds * LR
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What is post-test probability?
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The subjective probabilities of the presence of a condition (such as a disease) after a diagnostic test.
Can be positive or negative, depending on whether the test falls out as a positive test or a negative test, respectively. |
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Equ for post-test probability
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Post test odds / (post test odds + 1)
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How do you calculate POSITIVE post-test probability using TN, TP, FN, FP?
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True positives / (True positives + False positives)
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How do you calculate NEGATIVE post-test probability using TN, TP, FN, FP?
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False negatives / (False negatives + True negatives)
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Questions:
Difference between PPV and +ve post-test probability? Diffence between pre-test probability and pre-test odds |
?????
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How do you calculate post-test probability from relative risk?
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pre-test probability * relative risk
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Define number needed to treat
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The number of patients you need to treat to prevent one additional bad outcome (death, stroke, etc.).
For example, if a drug has an NNT of 5, it means you have to treat 5 people with the drug to prevent one additional bad outcome. |
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Equ for NNT using absolute risk reduction (ARR)
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NNT = 1/ARR
The Absolute Risk Reduction (ARR); the NNT is the inverse of the ARR ARR = CER (Control Event Rate) - EER (Experimental Event Rate) |
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Equ for Converting Odds Ratios to NNTs
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NNT = (1-(PEER*(1-OR))) / ((1-PEER)*(PEER)*(1-OR))
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Equ for Converting Odds Ratios to NNTH
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NNH = ((PEER*(OR-1))+1) / (PEER*(OR-1)*(1-PEER))
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