Epidemiology & Communicable Diseases

Purpose of Epidemiology

Epidemiology is the study of populations to:

• Monitor the health of the population.

• Identify the determinants of health and disease in communities.

• Investigate and evaluate interventions to prevent disease and maintain health.

• Seeks to describe, quantify, and determine occurrences of diseases.

Some Early Epidemiologists

• James Lind: identified the effects of diet on disease

• Florence Nightingale: monitor disease mortality during the Crimean War

• Hippocrates: first epidemiologist

• John Snow: descriptive study on cholera outbreak in London

Epidemiology is the…

• Study of the distribution and factors that determine health-related states or events in a population.

  • Information is used to control health problems.

Epidemic

A disease occurrence that clearly exceeds the normal or expected frequency in a community or region.

• Example: Small pox in Africa, monkey pox

Pandemic

A epidemic that progresses to worldwide distribution (HIV, bubonic plague, COVID-19).

Endemic

Always, present, manageable, does not disrupt society.

• Example: Influenza (the flu), Malaria, Syphilis

Epidemiologic Triangle

• Host: Susceptible human or animal that carries the diseases.

  • Ex: demographics, immunity, disease history

• Agent: A factor that causes or contributes to health problems.

  • Ex: virus, chemical, trauma

• Environment: external factors that influence the host.

  • Ex: pollution, psychosocial environment, climate

Theories of Causality in Health and Illness

Causality is the relationship between a cause and its effect.

• Chain of causation

• Causation in noninfectious disease: such as cancer and diabetes: environmental exposure and potential health outcomes.

• Multiple causations

• Web of Casuality

Web of Causality

• Recognizes the complex interrelationships of many factors interacting, sometimes in subtle ways, to increase or decrease the risk for disease or event.

• Relationships are sometimes mutual, with lines of causality going in both directions.

• Encompasses multifactorial causes of health problems and issues.

• Has been adapted to study the causation of both infectious and noninfectious diseases.

Immunity

A host’s ability to resist a particular infectious disease-causing agent.

Cross Immunity

• Acquired from past exposure to a related pathogen or its antigens.

• Ex: Protection against SARS-COV2 from past exposure to COVID-19; Small pox vaccine used to treat monkey pox.

Passive Immunity

• Short term/temporary protection

• Person is given antibodies

• Ex: Newborn receives antibodies from mother; injection of snake venom.

Active Immunity

• Long term protection

• Can be acquired naturally/artificially

• Ex: History of disease/vaccination

Herd Immunity

The resistance to the spread of a contagious disease within a population that results if a sufficiently high proportion of individuals are immune to the disease, especially through vaccination.

• Immune people outnumber the susceptible people.

• Level varies with diseases.

• Depends on risk

Risk

• Probability that a disease or unfavorable health condition will develop.

• Directly influenced by biology, environment, lifestyle, and system of health care.

• Risk Factors: negative influences.

• Epidemiologists studying population at risk: collection of people among whom a health problem has the possibility of developing because certain influencing factors are present or absent or because there are modifiable risk factors.

• Risk of disease name with or without risk factor 1:1 considered relative risk of 1.0.

• Relative risk > 1.0 indicates greater likelihood of acquiring disease.

• Relative risk of 2.5 means that exposed group is 2.5 time likely more to acquire the disease than the unexposed group.

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**Relative risk ratio = Incidence in exposed group / Incidence rate unexposed group**

Primary Prevention: Natural History of a Disease

Health Promotion & Education:

• May include:

  • Nutrition counseling—diabetes

  • Sex education—pregnancy

  • Smoking cessation—lung cancer

Health Protection:

• May include:

  • Improved housing and sanitation—waterborne diseases

  • Immunizations—communicable diseases

  • Removal of environmental hazards—accidents

Secondary Prevention: Natural History of a Disease

Early Diagnosis:

• The third stage in the natural history of disease, the early pathogenesis or onset stage:

  • Screening programs—breast and testicular cancer, vision and hearing loss, hypertension, tuberculosis, diabetes.

Prompt Treatment:

• Initiate prompt treatment.

• Arrest progression.

• Prevent associated disability,

Tertiary Prevention: Natural History of a Disease

Rehabilitation:

• Reduce the extent and severity of a health problem to minimize disability.

• Restore or preserve function.

Primary Prevention:

• Health Promotion and Education:

  • Training for employment—homeless population.

  • Group treatment and rehabilitation—adolescent drug users.

  • Food, shelter, rest/sleep, exercise

• Health Protection:

  • Health services

  • Immunization as needed

Sources of Information for Epidemiological Study

Existing Data:

• Routinely collected data (census data, vital records, surveillance data)

• Reportable diseases

• Disease registries (e.g., ALS, Rapid Response Registry, WTC)

• Surveillance systems (monitors diseases to develop and evaluate control strategies)

• Environmental monitoring (hazards in the environment)

• National Center for Health Statistics

• Health Surveys

• Centers for Disease Control and Prevention Reports

Informal Observational Studies:

• Raises questions and suggests hypotheses for larger-scale investigations.

Scientific Studies:

• Epidemiologic Studies

Descriptive Epidemiology

Person:

• Race, sex, age, education, occupation, income, and marital status.

Place:

• Examine geographical patterns.

Time:

• Secular trends

• Point epidemic

• Cyclical time patterns (seasonal fluctuation; calendar events)

• Non-simultaneous; event-related clusters

What is the goal of descriptive epidemiology?

Identify the cause of health problems and develop measures to prevent illness.

• Observe and describe patterns of health-related conditions that occur naturally:

  • Data on Measles Immunizations

• Counts:

  • # of deaths due to specific disease.

  • Time delay to gather data.

• Rates:

  • Proportion of people with given health problem.

  • Total number of people is denominator.

Rates: Incidence

• Refers to all new cases of a disease or health condition appearing during a given time.

• The numerator is all new cases, denominator population is at risk for a specific period of time.

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**New Cases / Person at Risk**

Rates: Prevalence

• All people with a particular health condition in a given population at a given point time.

• Period prevalence rate: the prevalence rate over a defined period of time.

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**Prevalence Rate = # of persons with a characteristic / Total number in population**

Analytic Epidemiology seeks to…+ Studies

Identify associations between a particular human disease or health problem and its possible causes.

• Prevalence Studies:

  • Describes patterns of occurrence.

  • Same point in time and in same population.

  • Examines casual factors and based on inferences from a single examination.

• Case-Control Studies:

  • Compares people who have health or illness condition (number of cases with the condition) with those who lack this condition (controls)

  • Retrospective—begins with the cases and looks back over time.

• Cohort Studies:

  • Group of people who share a common experience in a specific time period (elderly, employees of specific industry)

  • Often used with environmental hazard exposures

  • The people are the focus of the study.

Casual Relationships

Cross-Sectional Study:

• Explore health condition’s relation to other variables (broken window index).

Retrospective Study:

• Looks backward into time to find casual relationships.

• Uses existing data.

Prospective Study:

• Looks forwards to find casual relationship

• Cancer Prevention Study

Experimental Study:

• Investigator control or changes factors suspected of causing the condition and observes results.

• Used to confirm observational studies.

Applications of Epidemiology in Community-Oriented Nursing

Examples of Nursing Positions that Use Epidemiology:

• Nurse epidemiologist

• School nurses

• Communicable disease nurse

• Environmental risk communicators

• Hospital infections control nurse

All nursing documentation on patient charrs is an important source of data for epidemiologic reviews

Global Impact

According to the WHO, three disease are responsible for all infectious diseases each year (approximately 5 million):

• HIV/AIDS

• TB

• Malaria

• COVID-19 in 2020~

National Impact

Infectious diseases of concern in the U.S:

• Sexually transmitted diseases (including HIV)

• Mosquito-borne illnesses (Zika and Dengue)

• Whooping Cough

• Hepatitis (A, B, C)

• TB

• Influenza and pneumonia (vaccinations)

• Measles (vaccinations)

• COVID-19 (EUA vaccines)

Emerging Infectious Diseases

Diseases in which the incidence has increased in the past several decades or has the potential to increase in the future.

• Ebola virus

• MRSA

• HIV/AIDS

• SARS-Corona Virus

• Hantavirus (pulmonary syndrome)

Re-Emerging Infectious Diseases

Diseases that once were a major health problem globally or in a specific country and then declined, but are becoming significant health problems again:

• TB

• Malaria

• Syphilis

• Whooping Cough

Mode of Transmission

Vertical Transmission:

• Mother to child. (breastfeeding and utero)

Horizontal Transmission:

• Direct: direct contact or droplets (coughing or sneezing)

• Indirect: transmitted by fomites (insect, water, food, inanimate objects)

Vector-Borne Transmission:

• Medical transmission—does not require infectious organisms to multiply

• Biological transmission—requires an incubation period

Airborne Transmission:

• Suspended in the air or cling to inanimate objects. (e.g., TB, flu)

Foodborne Diseases

Infection:

• Results from bacterial, viral, or parasitic infection of food.

• Examples: Salmonella, Shigella, E.coli (food poisoning)

• Accompanied by an immune response with antibodies.

Intoxication:

• Production of toxins from bacteria.

• Example: Botulism

• Commonly occurs when cooked food is left out or by a food preparer.

• Toxins are difficult to identify.

Waterborne Diseases

• An outbreak occurs if two or more persons experience a similar illness after consuming contaminated water.

• Examples:

  • Hepatitis A

  • Cholera

  • Typhoid Fever

  • Bacterial Dysentery

Vector-Borne Diseases

Illness for which infectious agents are transmitted by a carrier (vector):

• Lyme disease (tick)

• Rocky Mountain spotted fever (tick)

• Malaria (mosquitos)

• Zika Virus (mosquitos)

Prevention and control of vector-born diseases:

• Prevent exposure

• Use repellants

• Vector control

Zoonoses Disease

An infection transmitted from a vertebrate animal to a human.

• Ex: Rabies

Parasitic Diseases

• More prevalent in tropical climates and countries with inadequate prevention and control methods.

• Intestinal parasitic infections.

• Parasitic opportunistic infections

Healthcare Associated Infections

• Infectious acquired during hospitalization or any health care setting.

  • May involve patient, health care workers, visitors.

• Also called nosocomial infections, hospital-acquired infections

• UTI, surgical infections, and pneumonia are the most common.

  • Bacteria: staph (blood), E.coli (UTI), enterococci (blood, UTI, wound), pseudomonas (all)

  • Universal Precautions.

HIV, Hepatitis, & Sexually Transmitted Diseases

• Often acquired through behaviors that can be avoided or changed.

• Nursing actions should focus on disease prevention.

  • Vaccine administration, early detection, or teaching clients about abstinence or safer sex.

• Infected individual can transmit to others.

Factors Associated with Risk for STIs

• Younger than 25 years

• Member of a minority group

• Residing in a urban setting

• Being impoverished

• Substance use

• Unsafe sex practices

• Women have higher risks of complications from STIs (PID, sterility, cancer)

• Can be transmitted to neonate

Gonorrhea

• Second most reportable notifiable disease.

• Increasing (transmission or reporting).

• Men have symptoms: drainage from penis.

• Women: are often asymptomatic.

• Antimicrobial resistance: cephalosporin with azithromycin or doxycycline.

• Can be transmitted to neonates during delivery: opthalmic prophylactic agent.

Syphilis

• 3 Stages:

  • Primary (charce)

  • Secondary (rash, fever, sore throat)

  • Latent (tertiary syphilis associated with neurological changes)

• Treatment: Penicillin

**don’t treat unless definitely possible.

Chlamydia

• Most commonly reported STD.

• Silent with serious complications.

• Specific screening recommendations by the CDC.

Herpes Simplex Virus-2 (genital herpes)

• No cure, but can control symptoms.

Human Papillomavirus Infection (HPV)

• HPV vaccine

HIV/AIDS

• No cure

• Prevention, treatments, and care focuses on early testing.

• Rapid testing.

• Positive status can be controlled with medications.

Levels of Prevention: HIV/AIDS

Primary Prevention:

• Use of condoms

• Clean needle sharing

• Universal precautions

Secondary Prevention:

• HIV counseling and testing

• Early diagnosis with rapid testing

• Screen for co-morbidities

Tertiary Prevention:

• Medication control

• Education to prevent re-infection and reduce co-morbidities

STIs & Ethics

• Access to healthcare

• Routine testing

• Legal implications for transmission

• Confidentiality, privacy, stigma, and discrimination

• Infected healthcare workers

Preventing STIs

Requires diverse and multidisciplinary interventions:

• Parents, families, schools. religious organizations, health departments, community agencies, and media.

Educational programs provide adolescents with the knowledge and skills to:

• Refrain from early onset of sexual intercourse.

• Make informed decisions related to sexual behavior and health.

• Increased the use of contraceptive measures.

Hepatitis A Virus

• Transmitted through fecal-oral route.

• Sources: water, food, or sexual contact.

• Treatment: Inactivated Hep A vaccine administered in 2 doses.

Hepatitis B

• Spread through the blood and body fluids; can survive at room temperature for at least 1-week.

• Treatment: 3 doses of the vaccine.

Hepatitis C

• Spread through blood or boy fluids.

• Most common chronic blood-borne infection in the U.S.

• Can be asymptomatic

• Leading cause of chronic liver disease, end-stage liver disease, liver cancer, and liver transplants in the U.S.

• Prevention: testing for people born between 1945 and 1965, IV drug abuser, organ transplant or blood donations before 1992, HIV/AIDS, liver, born to GCV+ mothers.

• No vaccine, but there is a cure.

Tuberculosis

• Spread by droplets

• Poor nutrition, health status, and chronic disease can contribute to developing active disease.

• Communicability depends on the length of exposure as well as proximity.

• Incubation period: 10 to 12 weeks

• Latent Phase: can last for many years

• Active Phase: symptoms are evident such as cough, fatigue, loss of appetite, weight loss, and night sweats.

  • Chest x-ray shows infiltrate; positive for PPD

  • Control and elimination of TB

  • Screening can be detected through skin or blood test

Control and Elimination of TB

WHO characterizes TB burdens into 3 classifications:

• Multidrug-resistant TB

• Clients with HIV and TB

• TB case management

Screening Tests:

• Skin testing with purified protein derivative (PPD)

• Two step testing

• Interferon gamma release assays (IGRA)

• Blood Test

• For people who will not return for reading or BCG

• Lack of adherence to medication (taken over 3 to 6 months)

Positive tests:

• Followed up by chest radiography for persons with a positive skin reaction and pulmonary symptoms.

Isoniazid (INH) for those exposed and infected but no evidence of active disease.

Responds well to long-term treatment: 

• First Line Drugs: greatest activity against active bacteria

• Second Line Drug

•Directly Observed Treatment (DOT)

Infectious Diseases of Bioterrorism

Anthrax:

• Acute bacterial disease that affects mainly the skin (cutaneous or respiratory tract (inhalation)

• Case Fatality: 5% to 20% for cutaneous; 100% for inhalation

Smallpox:

• Variola virus transmitted person to person

• Routine immunization not recommended

• Risks associated with smallpox vaccination

• Ring Vaccination Strategy

Nursing Process for Communicable Disease Control l

• Assessment: Case identification, case finding, comprehensive, no assumptions, community’s need for surveillance or new or improved control programs

• Planning: Assisting with immunizations, symptoms relief, controlling disease if present, limiting exposure, collaboration

• Implementation: Service delivery, supervision of staff, primary prevention education for future infections, record keeping and reporting

• Evaluation: What was the outcome? Did you get what you expected?

Communicable Diseases: CHN’s Role

Help with investigating reportable communicable diseases using a systematic approach. 

• Review information

• Clarify disease is suspect or lab confirmed

• Review case definition

• Review disease information

• Use specific questionnaires when available

At all levels of prevention, the nurse functions in the following roles:

• Counselor

• Educator

• Advocate

• Case manager

• Primary care provider

Primary Prevention: Communicable Diseases

Education:

• Use of mass media

• Targeting meaningful health messages to aggregates.

Immunization:

• Vaccine preventable diseases and schedules.

• Assessing immunization status of community (possible barriers); planning and implementing immunization programs.

• Adult immunizations.

Vaccine-Preventable Diseases

Routine recommended childhood immunizations includes: 

• Hepatitis A & B

• Diphtheria

• Pertussis

• Measles, mumps, rubella (MMR)

• Rotavirus

• Polio

• Haemophilus influenza

• Meningococcal conjugate

• Varicella (chickenpox)

• Influenza (seasonal)

• Human papillomavirus

• Covid-19 

Secondary & Tertiary Prevention: Communicable Diseases

Secondary Prevention:

• Screening

• Case and contact investigation; partner notification

Tertiary Prevention:

• Isolation and quarantine:

  • Control transmission by health care workers

  • Safe handling and control of infectious wastes

Reporting Communicable Diseases

• CDC and WHO offer guidelines for investigative procedures.

• Diseases are reported to local health authorities, and initial point of contact is investigated.

• Reportable diseases are reported to the State Health Department and then to CDC

• Each state has a disease report form

• Any outbreak

• Unusual disease

Disease Reporting in Georgia

• All physicians, laboratories and other health care professionals are required by law to report conditions listed under the Notifiable Disease Reporting Requirements.

• Both laboratory and clinical diagnoses are reportable within specified time intervals.

  • Most diseases are reportable within 7 days.

• Diseases that need to be reported immediately are done through a telephone call to the public health district.

Communicable Diseases: Ethical Issues

Health Care Access:

• Cost

Enforced Compliance:

• Direct observation therapy (DOT)

Confidentiality and Discrimination:

• Partner notification