Clinical Preventive MedicineClinical Preventive Medicine

Wang Min （王敏）School of Public health and general medicinSchool of Public health and general medicin

ee

Clinical Preventive Medicine

（ CPM ） those personal health services provided in the

context of clinical medicine, the purpose of which is to maintain health and reduce the risk of disease and untimely disease.

Preventive services were divided into three categories

Screening tests （筛检） Counseling interventions （健康咨询） and health e

ducation （健康教育） The Periodic Health Examination （周期性健康检

查） Nutrition guidance （营养指导） Immunizations （免疫预防） Chemoprophylaxis （化学预防）

Screening

Screening is a public health service in which members of a defined population, who do not necessarily perceive they are at risk of, or are already affected by a disease or its complications, are asked a question or offered a test, to identify those individuals who are more likely to be helped than harmed by further tests or treatment to reduce the risk of a disease or its complications.

The Purpose of Screening:

to find persons with risk factors in which preventive interventions could be used or to identify individual with early or asymptomatic treatable disease.

The principle of screening test:1.The disease should be an important health problem ，

having severe consequences or high prevalence2. The detection of rare diseases may lead to high cost-

benefit ratios. 3.The epidemiology and natural history of the condition,

including development from latent to declared disease, should be adequately understood and there should be a detectable risk factor, disease marker, latent period or early symptomatic stage.

4.An effective preventive intervention or treatment should be available.

5.All the cost-effective primary prevention interventions should have been implemented as far as possible.

The test

1.There should be a simple, safe, precise and validated test.

2.The distribution of the test values in the target population should be known and a suitable cut-off level defined.

3.The test should be acceptable to the population 4.There should be an agreed policy on the further

diagnostic investigation of individuals with a positive test result and on the choices available to those individuals.

The treatment

1.There should be an effective treatment or intervention for patients identified through early detection, with evidence of early treatment leading to better outcomes than late treatment.

2.There should be agreed evidence-based policies covering which individuals should be offered treatment and the appropriate treatment to be offered.

3.Clinical management of the condition and patient outcomes should be optimised by all health care providers prior to participation in a screening programme.

screening test must satisfy two major requirements to be considered effective:

1The test must be able to detect the target condition earlier than without screening and with sufficient accuracy to avoid producing large numbers of false-positive and false-negative results (accuracy of screening test ).

2 Screening for and treating persons with early disease should improve the likelihood of favorable health outcomes (e.g., reduced disease-specific morbidity or mortality) compared to treating patients when they present with signs or symptoms of the disease (effectiveness of early detection ).

Pros and cons of screening

Advantages Disadvantages

Improved prognosis for some Cases Less radical treatment Resource savings Reassurance

Longer morbidity for cases whose prognosis is Unaltered Overtreatment of questionable abnormalities Resource costs  False reassurance of false negative people Anxiety and hazard for false positive cases Hazard of screening test

Counseling interventions

are those in which the patient receives information and advice regarding personal behaviors (e.g., diet) that could reduce the risk of subsequent illness or injury. The Task Force did not consider counseling that addresses the health-related behaviors of persons who have already developed signs and symptoms of the target condition.

Counseling interventions and health education

1. Use plain language.

2.Start with the most important information

first.

3.Use repetition to reinforce your message.

4.Ask the patient to restate the message.

5.Provide an opportunity for questions.

Counseling/Education about Disease

• Be specific and concrete. • Start with the most important information

first. • Use repetition to reinforce your message. • Ask the patient to restate the message. • Provide opportunities for questions.

What Works? • Provide information – Use multiple forms of information. – Answer questions. • Reward patients for positive behavioral change. • Tailor the intervention to the patient’s needs. • Provide feedback about the change in health status measure.

Example

What is Hypertension? Why does hypertension need to be

treated? How is hypertension treated? Managing and Preventing Hypertension • BMI 18.5 – 24.9 kg/m2

Exercise – 30 minutes per day most days of week “Moderate” alcohol consumption – Men 2 drinks or fewer per day – Women 1 drink or fewer • Increase dietary intake potassium – 3500 mg a day • Increase dietary intake potassium – 3500 mg a day

History RPHE developed with consideration of

overall financial impact and patient considerationsSpecific costs not calculatedspecific patient considerations not elicited

but board members served as surrogates

Periodic Health Examinations(RPHE: 周期性健康体检 )

The RPHE

“These recommendations are provided only as assistance for physicians making clinical decisions regarding the care of patients.” “Can not substitue for the individual judgement brought to each clinical situation by the patient’s family physician.”

AAFP Recommendations

SR Strongly Recommend: Good quality evidence exists which demonstrates substantial net benefit over harm; the intervention is perceived to be cost effective and acceptable to nearly all patients

R Recommend: Although evidence exists which demonstrates net benefit, either the benefit is only moderate in magnitude or the evidence supporting a substantial benefit is only fair. The intervention is perceived to be cost effective and acceptable to most patients.

AAFP Recommendations

NR No Recommendation Either for or Against: Either good or fair evidence exists of at least a small net benefit. Cost-effectiveness may not be known or patients may be divided about acceptability of the intervention.

RA Recommend Against: Good or fair evidence which demonstrates no net benefit over harm.

AAFP Recommendations

I Insufficient Evidence to Recommend Either for or Against: No evidence of even fair quality exists or the existing evidence is conflicting.

I-HB Healthy Behavior is identified as desirable but the effectiveness of physician’s advice and counseling is uncertain.

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Health Examination ProcessHealth Examination Process

Definitionof needs

Process:- planning- implementation- health education- recommendat-ions

Results Evaluation

Example

Immunization

Terms Immunization – conferring immunity by

artificial means Vaccination – conferring immunity to a

disease using a vaccine or special antigenic material to stimulate the formation of appropriate antibodies

Vaccine – preparation of antigenic material – stimulates Ab production – confers active immunity

vs.disease Latin “vacca” = cow (from cowpox)

ImmunizationUsing vaccines or antibody-containing

preparations to provide immune protection vs. specific diseases

PassivePreformed antibodies - another hostProtect individual exposed to disease

Active (vaccines)Modified / purified pathogens or their

productsStimulate host to produce own specific

immunity

Passive Immunization

IgG - immediate protection - no memory Standard Igs (human, animals) Non-specific

Pooled plasma from donors Igs vs. many common viruses

Human hyperimmune serum (high titre) SpecificFrom donor c. high titre Abs to specific virusAgainst specific (single) virus

Passive Immunization

Indications: Exposure has occurred, or is expected to occur soon No effective vaccine exists or time req’d too short Underlying illness – prevents admin. vaccineE.g. uses: Standard Ig – Congenit./acq. Ig deficiency, prevent Hep

A Rabies Ig (HRIg) – post-exposure prophylaxis VZ Ig – post-exposure prophylaxis if at high risk CMV Ig – passive imm. renal transplant recipient

Vaccines - Active

Injection of viable / non-viable pathogens or purified pathogen productsResponse as if being attacked by intact

organism Live / inactivated / DNA vaccines Effective starting after ~2 wks to few

months Prolonged immunity <-- own antibodies

produced

Active vaccine - Live attenuated pathogens

Multiplies inside human host & provides strong antigenic stimulation

Provides prolonged immunity (yrs to life), often with single dose

Vaccine often provides cell-meditated immunity

Disadvantage – can revert to virulent form--> Do not give to immunocomprom., pregnant

Active - Killed micro-organism

Does not multiply in human host Immune response depends on Ag content

of vaccine Multiple doses of vaccine required with

subsequent booster doses Provides little cell-mediated immunity No possibility of a vaccine-assoc. infection

Active - Microbial extracts

Extracted molecules (Ags): from pathogen from acellular (non-infectious) filtrate of

culture medium in which org. grown recombinant DNA techniques

Vaccines can be prepared with toxoids (=derivatives of exotoxins) Used when pathogenicity of org. is due to secreted

toxin E.g., tetanus, diphtheria

Active - Toxoids

Derivatives of bacterial exotoxins Rendered non-toxic But remain immunogenic Admin – IM, SC E.g.

TetanusDiphtheria

Attenuated pathogen

Killed pathogen

Microbial extract / product

Bacterial Diseases

Typhoid (PO)

BCG (M. bovis)

(Salmonella)

Typhoid fever

Cholera

Pertussis

Plague (Y. pestis)

Anthrax

B. pertussis Ag

*Hib

Diphtheria (Tox.)

*Meningococcal

*Pneumococcal

Tetanus (Tox.)

Viral Diseases

Measles

Mumps

Rubella

Chickenpox

Polio (Sabin - PO)

Yellow fever

Polio (Salk)

Hep. A

Influenza

Rabies

Japanese encephalitis

Hep. B

Vaccine components

Age & Immunity

Passive immunity from motherMaternal IgG passes the placentaBefore and at birth – IgG presentBreast milk – secretory Abs (GI & resp. tract)

Active Immunization Infant begins to produce Abs in 1st yrStart immunization at 2 months (usually)

Elderly --> weaker immune response

Problems with vaccines

Localized - at site of injection Anaphylaxis to Ag or non-microbial

content vaccine (eggs) Contamination with pathogen Reversion of attenuation Lack of efficacy if another concurrent

infection (rubella & polio vaccine) Organisms with lots of serotypes

Vaccine development

Properties of good candidate: Organism – causes significant illness Organism – 1 serotype Organism – no oncogenic potential Antibodies – block infection / systemic

spread Vaccine – heat stable

Success of immunization program

Composition of vaccine Life-long immunity Administration

TimingSiteConditions

Immunization - ? When Birth - Hep B Childhood - DTP, Polio, Hep B (2,4,6/12),

Hib (2,4,12), MMR (12/12), DT (15 -19yrs)

Adult - Boosters, 50yrs – DT(unless booster <10 yrs)

Travellers - Yellow fever, Typhoid Non-immune ♀ - MMR Risky lifestyle - Hep B, Heb A Aboriginal & >50yrs – Influenza (yearly),

or non-Abor & > 65 yrs - Pneumococcus (5-yearly)

Standard vaccination schedule

For footnotes, see: http://www.dh.sa.gov.au/pehs/Immunisation/aust-vacc-schedule-web.pdf

From: http://www.dh.sa.gov.au/pehs/communicable-diseases-index.htm

Recommended Childhood and Adolescent Immunization Schedule

Other target groups

From: Vaccine brochure, SmithKline Beecham

Challenges Predicting the protective ags

e.g., Influenza (haemagglutinin & neuraminidase variants)

Not knowing the virulence determinantse.g., Tuberculosis

Antigenic variation Promoting T-cell stimulation

Vaccine Safety – New Challenges…

1.More vaccines to oversee

2.Investment not kept up with demands

3.Benefits “invisible” as

diseases disappear

4.Real and perceived risks of vaccine more apparent

5.Public trust at stake

Chemoprophylaxis

Chemoprophylaxis as primary prevention

refers to the use of drugs or biologics taken

by asymptomatic persons to reduce the risk

of developing a disease.

The use of chemoprophylaxis is limited primarily by two factors:

1.All medications have the potential to cause side effects. In general, chemoprophylaxis should be initiated only when the benefits of treatment outweigh the risks.

2.The cost associated with chemoprophylaxis may be prohibitive, particularly when the cost of treatment is high or the incidence of the target disease is low. Many forms of chemoprophylaxis are therefore not cost-effective.

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