Chapter 7 Intro to Public health Communicable Disease

Epidemic is

"The unusual occurrence in a community of disease, specific health related behavior, or other health related events clearly in excess of expected occurrence" (epi= upon; demos= people) Epidemics can occur upon endemic states too.

Rabies

- A virus transmitted through saliva of infected animals - 20-60 day incubation period - Once central nervous system involved, proceeds inevitably to death within 2 weeks - Racoons, skunks, bats common source in US - What source in other countries? PHILIPPINES/VIETNAM DOGS

What Options Are Available for the Control of HIV/AIDS?

- Currently, we are unable to eradicate HIV/AIDS like we have eradicated smallpox - However, we are able to reduce the load of virus through drug treatment and preventing the transmission of the disease through a variety of public health interventions Potential interventions depend upon the route of transmission being considered

Table 7-2 Eradication of Human Diseases: Measles

- Disease is limited to humans, i.e., no animal reservoir? YES - Limited persistence in the environment? YES - Absence of long-term carrier state? Yes, but may occur in immune-compromised individuals - Long-term immunity results from infection? Yes, but may not be sustained in immune-compromised individuals - Vaccination confers long-term immunity?Yes, but may not be sustained in immune-compromised individuals - Herd immunity prevents perpetuation of an epidemic? YES - Easily diagnosed disease? No - may be confused with others - Vaccination effective postexposure? NO

How Can Public Health Efforts Maximize Effectiveness of Treatment and Prevent Resistance?

- Drug resistance occurs due to overuse of prescribed antibiotics, over-the-counter sales of antibiotics, and widespread use of antibiotics in agricultural animals - Directly observed therapy (DOT) can be effective treatment, even in the presence of drug resistance

How Can Barriers Against Disease be Used to Address the Burden?

- Insecticide-impregnated bed nets decrease the rate of malaria transmission - Condoms prevent sexually transmitted diseases - Masks reduce the spread of disease in healthcare institutions - Isolation and quarantine are used to separate individuals with disease from the healthy population to prevent exposure example: not going to work/ school to help minimize other people to get expose

Characteristics of a Disease That Make Eradication Possible

- No animal reservoir - Short persistence in environment - Absence of long-term carrier state - The disease produces long term immunity - Vaccination produces long term immunity - Herd immunity protects those who are susceptible - Easily identified disease - Effective post exposure vaccination

What Public Health Tools are Available to Address the Burden of Communicable Diseases?

- Physical Barrier protections- isolation, quarantine - Immunizations - Screening and case finding of unsual disease - Treatment and contact treatment - Efforts to maximize effectiveness of treatments and prevent resistance to treatment

How Can Screening and Case Finding be Used to Address the Burden?

- Screening controls the spread of a many infections HIV, STDs, tuberculosis, syphilis - Screening for communicable disease has been linked with case finding - Confidential interviewing of those diagnosed with the disease and asking for their recent close physical or sexual contacts - Key to the control of syphilis and TB both before and after the availability of effective treatment

Medications to treat influenza and modestly shorten the course of the disease have been developed

- Temporarily slows the spread of new strains to provide more time to develop vaccines to target it - However, widespread use has already lead to resistance

Eradication is

- Termination of all transmission of infection by the extermination of the infectious agent through surveillance and containment. - An absolute process, an "all or none" phenomenon, restricted to termination of infection from the whole world.

Reproduction ratio (R0)

- The number of new cases one individual with the disease generates on average over the course of its reproductive period - Measure of inherent transmissibility - Depends heavily on the route of transmission as well as the presence or absence of asymptomatic transmission

How Can Treatment of Those Diagnosed and Their Contacts Help to Address the Burden of Communicable Disease?

- Treatment of symptomatic disease may in and of itself reduce the risk of transmission Reduces infectivity - Epidemiological treatment- treatment of contacts Effective in controlling the number of individuals with the disease Used with sexual partners of patients with STDs

Koch's Postulates: Four Conditions to Establish Contributory Cause

1. The organism must be shown to be present in every case of the disease by isolation of the organism 2. The organism must not be found in cases of other disease 3. Once isolated, the organism must be capable of replicating the disease in an experimental animal 4. The organism must be recoverable from the animal

Definition of communicable diseases

A communicable disease is an illness due to a specific infectious (biological) agent or its toxic products capable of being directly or indirectly transmitted from man to man, from animal to man, from animal to animal, or from the environment (through air, water, food, etc..) to man.

What Options Are Available for the Control of Rabies?

A multicomponent vaccination strategy has been very successful in preventing the development of rabies in humans - Vaccines are administered to individuals who are bitten by suspicious species of wild animals - Vaccination of cats and dogs - The recent development of an effective oral vaccine that is administered to wildlife through baits is thought to be reducing the number of infected animals

Table 7-3 Potential for Eradication of HIV/AIDS

ALL ANSWERS IS NO - Disease is limited to humans? - Limited persistence in the environment? - Absence of long-term carrier state? - Long-term immunity results from infection?Vaccination confers long-term immunity? - Herd immunity prevents perpetuation of an epidemic? - Easily diagnosed disease? - Vaccination effective postexposure?

Asymptomatic transmission

Ability to transmit the disease while humans or animals are free of symptoms

Spread of Communicable disease Indirect

Airborne Vehicle Vector Inanimate Intermediate host

Table 7-2 Eradication of Human Diseases: Smallpox

All the answer is YES Disease is limited to humans, i.e., no animal reservoir? Limited persistence in the environment? Absence of long-term carrier state? Long-term immunity results from infection? Vaccination confers long-term immunity? Herd immunity prevents perpetuation of an epidemic? Easily diagnosed disease? Vaccination effective postexposure?

Pandemic

An epidemic usually affecting a large proportion of the population, occuring over a wide geographic area such as a section of a nation, the entire nation, a continent or the world, e.g. Influenza pandemics.

Route of transmission

Anatomical and physical methods for transmission from person to person and from animal species to humans

Ring Vaccination

As used in the smallpox eradication program, immediate vaccination of populations in surrounding geographic areas after identification of a case of disease.

Antiobiotic resistance

Bacteria get their resistance from genes that produce proteins that: - Inactivate the antibiotic - Pump the antibiotic out of the cell - Allow them to function in spite of antibiotic • Comes from genes − 1. mutation and selection − 2. from plasmids carrying mutation

Agent

Biological agents Physical agents Chemical agents Nutrient agents Mechanical agents Social agents

Burden of Disease years expectation

By the year 2020, noncommunicable diseases are expected to account for seven out of every ten deaths in the developing regions, compared with less than half today. Injuries, both unintentional and intentional, are also growing in importance and by 2020 could rival infectious diseases as a source of ill-health.

Table 7-1 Methods of Transmission of Human Disease and examples contaminated articles (fomites)

Chickenpox, common cold, influenza

What is the Burden of Disease Caused by Communicable Diseases?

Communicable disease may be caused by a wide variety of organisms, such as bacteria, viruses, or parasites For many centuries, communicable diseases were the leading cause of death and disability among all ages, but especially among the young and the old May cause great epidemics Can also become endemic and become routine causes of death

Host

Demographic characteristics Biological characteristics Socioeconomic characteristics

What is DOT

Directly observed therapy ex. TB DOT ensures complete adherence to treatment by observing individuals taking treatment at certain intervals

Table 7-2 Eradication of Human Diseases: Polio THIS HAPPENS ONLY IN GEOGRAPHIC AREAS

Disease is limited to humans, i.e., no animal reservoir? YES Limited persistence in the environment? YES Absence of long-term carrier state? Yes, but may occur in immune-compromised individuals Long-term immunity results from infection? Yes, but may not be sustained in immune-compromised individuals Vaccination confers long-term immunity? Yes, but may not be sustained in immune-compromised individuals Herd immunity prevents perpetuation of an epidemic? YES Herd immunity prevents perpetuation of an epidemic? YES Easily diagnosed disease? YES/NO Vaccination effective postexposure? NO

Table 7-4 Mode and Chances of Transmission of HIV and Existing Interventions Mother-to-child transmission

ESTIMATED TRANSMISSION RATE PER EXPOSURE 15% to 40% higher in developing countries Highest rate of transmission at time of vaginal delivery POTENTIAL INTERVENTIONS Cesarean delivery Drug treatment during pregnancy and at time of delivery for mother and child

Table 7-4 Mode and Chances of Transmission of HIV and Existing Interventions Blood transfusion Blood and blood products, such as pooled blood products previously used in US by hemophiliacs

ESTIMATED TRANSMISSION RATE PER EXPOSURE Contaminated blood over 90% chance of transmission with infected blood; pooling of blood dramatically increases infection risk POTENTIAL INTERVENTIONS Screening of blood to detect HIV early Use of individual's own blood for surgery

Table 7-4 Mode and Chances of Transmission of HIV and Existing Interventions Needle stick exposures Healthcare occupational risk

ESTIMATED TRANSMISSION RATE PER EXPOSURE Less than 0.5% of HIV-positive needle sticks result in transmission POTENTIAL INTERVENTIONS Post exposure treatment with drugs established as effective prevention

Table 7-4 Mode and Chances of Transmission of HIV and Existing Interventions Injection drug use

ESTIMATED TRANSMISSION RATE PER EXPOSURE Less than 1% per episode of needle sharing POTENTIAL INTERVENTIONS Needle exchange program

Table 7-4 Mode and Chances of Transmission of HIV and Existing Interventions Sexual contact—anal higher than vaginal, which is much higher than oral

ESTIMATED TRANSMISSION RATE PER EXPOSURE Range from 0.1% to 10% per contact with unprotected receptive anal intercourse posing highest risk Vaginal male to female greater than female to male Circumcision reduces risk by half Other sexually transmitted diseases may increase risk - POTENTIAL INTERVENTIONS Latex condom Circumcision Abstinence Serial monogamy reduces spread compared to two or more concurrent partners

Table 7-4 Mode and Chances of Transmission of HIV and Existing Interventions Breastfeeding

ESTIMATED TRANSMISSION RATE PER EXPOSURE Very low per exposure, but up to 25% over year or more of breastfeeding POTENTIAL INTERVENTIONS Continuation of drug treatment reduces, but does not eliminate, transmission

Modern Koch's Postulates

Evidence of an epidemiological association Isolation of disease agent Transmissions to establish that an organism is a contributory cause of disease

Table 7-1 Methods of Transmission of Human Disease and examples Sexual transmission/open sores

Gonorrhea, syphilis, herpes genitalis, chlamydia, hepatitis B, HIV

Table 7-1 Methods of Transmission of Human Disease and examples breastfeeding

HIV

Table 7-1 Methods of Transmission of Human Disease and examples transfusions/blood/ contaminated needles

Hepatitis B and C

Table 7-1 Methods of Transmission of Human Disease and examples water/food

Hepatitis a, Cholera

Infectious Disease Model

Host, Environment, Pathogen

Epidemiologic triad

Host, agent, Environment

Prevalance interrelationship between incidence (cont'd)

If duration of disease is long and incidence is low, prevalence increases greatly relative to incidence. Example: HIV/AIDS prevalence

Incidence interrelationship between prevalance (cont'd)

If duration of disease is short and incidence is high, prevalence becomes similar to incidence. Short duration--cases recover rapidly or are fatal. Example: common cold

How Can Immunizations be Used to Address the Burden?

Immunizations strengthen the immune system to prevent or control disease Immunizations create herd immunity

What Options Are Available for the Control of Influenza?

Influenza A Medications to treat influenza and modestly shorten the course of the disease have been developed

Table 7-1 Methods of Transmission of Human Disease and examples Airborne-person-person

Influenza, SARS, measels, chicken pox, tubercolosis, common cold

Interrelationship Between Prevalence and Incidence

Interrelationship: P=ID The prevalance (P) of a disease is proportional to the incidence times the duration (D) of a disease

Figure 3-5 HIV incidence and prevalance United States, 1977-2006 printed from august 25,2012

It is important to know that each year HIV continues to grow

Endemic

It refers to the constant presence of a disease or infectious agent within a given geographic area or population group. It is the usual or expected frequency of disease within a population. (En = in; demos = people)

Burden of Disease is

It was previously thought that, as countries develop, noncommunicable disease replaced communicable disease as the main source of ill-health. However, there is now evidence that the poorest in developing countries face a triple burden of communicable disease, noncommunicable disease and socio-behavioral illness.

What is the Burden of Disease Caused by Communicable Diseases? Public health and medical interventions have and will continue to have major impacts on the burden of communicable diseases

Last half of 1900s saw a brief respite due to medical efforts to treat infections and public health efforts to prevent or eradicate infections The early 2000s have seen the return of infections that were previously under control, as well as the emergence of new diseases

Table 7-1 Methods of Transmission of Human Disease and examples Insects

Malaria, Lyme disease, west nile virus, yellow fever

Environment

Physical environment Biological environment Social environment

Table 7-1 Methods of Transmission of Human Disease and examples fecal/oral

Polio, salmonella

Incidence and prevalence of infectious diseases

Prevalence is a product of incidence x duration of disease, and is of little interest if an infectious disease is of short duration (i.e. measles), but may be of interest if an infectious disease is of long duration (i.e. chronic hepatitis B).

Spread of Communicable disease Direct

Reservoir: Man, Animal, Inanimate Susceptible Host: Man, Animal

Table 7-1 Methods of Transmission of Human Disease and examples transplacental

Rubella, HIV

Burden of Disease examples

Seasonal influenza kills more than 30,000 people per year in the United States

Burden of Disease spread of disease

The global burden of disease methodology shows that the epidemiological transition is already well advanced, suggesting that public health policy in poor countries, with its traditional emphasis on infectious disease, will need to adapt

What Factors Affect the Ease that a Communicable Disease is Transmitted?

Three factors have major impacts on transmission: - Route of transmission - Asymptomatic transmission - Reproduction ratio (R0)

What Public Health Tools are Available to Address the Burden of Communicable Diseases?

Vaccination for polio/measels and chicken pox

Live vaccines

attenuated organisms used to stimulate cell-mediated immunity and create long term protection

Influenza A

continues to mutate, creating new types against which previous infections and vaccinations have little or no impact - New live and attenuated vaccines are needed each year - Need 6 months lead time to produce the vaccine

Inactivated vaccine

dead organisms injected into patient to build immunity

herd immunity

general immunity to a pathogen in a population based on the acquired immunity to it by a high proportion of members over time. The more people vaccinated, the safer the non-vaccinated individuals will be - 80% req.

Passive immunity

inject antibodies into an individual for short term protection

Elimination is

is sometimes used to describe eradication of a disease from a large geographic region. Disease which are amenable to elimination in the meantime are polio, measles and diphtheria.

Virulence

is the degree of pathogenicity; the disease evoking power of a micro-organism in a given host. Numerically expressed as the ratio of the number of cases of overt infection to the total number infected, as determined by immunoassay. When death is the only criterion of severity, this is the case fatality rate.

Case fatality rate for infectious diseases

is the proportion of infected individuals who die of the infection. This is a function of the severity of the infection and is heavily influenced by how many mild cases are not diagnosed.

Elimination of a disease example

measles because this is a type of disease that comes back with less herd immunity geographically

Prevalence of an infectious disease

number of cases at a given time expressed as a percent at a given time. (number of cases already exist and becoming chronic)

Incidence of an infectious disease

number of new cases in a given time period expressed as percent infected per year (cumulative incidence) or number per person time of observation (incidence density). (number of new cases of an infectious disease)

Table 7-1 Methods of Transmission of Human Disease and examples Other animals

rabies, avian flu, anthrax, plague, other zoonotic disease

Eradication of a disease example

small pox that does not exist anymore because of edward jenner announced on 1979 by WHO 1980

Immunity

the ability of an organism to resist a particular infection or toxin by the action of specific antibodies or sensitized white blood cells.

Latent period

the period between exposure and the onset of infectiousness (this may be shorter or longer than the incubation period).

Incubation period

time from exposure to development of disease. In other words, the time interval between invasion by an infectious agent and the appearance of the first sign or symptom of the disease in question.

Asymptomatic

without symptoms, when referring to screening for disease, it implies the absence of symptoms of the disease being sought.