CH 11: Epidemiology

Communicable Disease

• infectious diseases that is transmissible from one human to another

Zoonotic Disease

Infectious diseases that humans acquire from animal sources

Incidence

The number of new cases of that disease in a defined population during a specific time period

Morbidity Rate

The number of new cases of a particular disease that occurred during a specified time period per a specifically defined population

Period Prevalence

The number of cases of the disease existing in given population during a specific time period

Point Prevalence

The number of cases of the disease existing in a given population at a particular moment in time

Mortality Rate/ Death Rate

The ratio of the number of people who died of a particular disease during a specified time period per a specified population

Sporadic Diseases

Diseases that occur only occasionally within the population of a particular geographic area

Epidemic Diseases

• Diseases that are always present, within the population of a particular geographic area

• Number of cases of the disease may fluctuate over time, but the disease never dies out completely

Examples of Endemic Diseases

• staphylococcal and streptococcal infections, STDs (gonorrhea and syphilis), common cold, influenza, chickenpox, mump [US- humans]

• Plague (Yersinia pestis), endemic among rats, prairie dogs, and other rodents

Epidemic

A disease that spreads quickly in a specific region

Pandemic

A disease that spreads quickly across a large geographical area

Epidemics in the Untied States within the past 35 years

• 1995: Polio

• 1966: Smallpox

• 1976: Legionnaire’s Disease

• 1976: Ebola

• 1978: Asprin use and Reye Syndrome

• 1981: HIV/AIDS

• 1993: E. coli

• 2001: Anthrax

• 2003: SARS

• 2014: Ebola

• HIV/HEP

Legionaire’s Disease (1976)

• present in water circulated through the air-conditioning system

• aerosols of organisms were inhaled by occupants

• hotels, hospitals, cruise ships, and supermarkets (misting of vegetables)

Escherichia Coli (1992-1993)

• contaminated hamburger meat in Pacific northwest

• approx. 550 diarrheal cases, 45 cases of kidney failure (hemolytic uremic syndrome), and several young children

• hamburgers were contaminated with cattle feces during slaughtering process

• hamburgers had not been cooked long enough, or at a high temperature, to kill the bacteria

Hantavarius Pulmonary Syndrome (1993)

• Native American reservations in the Four Corners region (Colorado, New Mexico, Arizona, and Utah)

• 50-60 cases with 28 deaths

• Sin Nombre virus

• Present in the urine and feces of deer mice

• aerosols were produced when residents swept up house dust contaminated with rodents droppings

Cryptosporidiasis (1993)

• diarrheal disease

• Milwaukee, Wisconsin

• drinking water contaminated with the oocysts of Cryptosporidium parvum (parasite)

West Nile virus (2002)

• occured throughout the United States

• 4,100 human cases, 284 deaths

• 16,000 birds died and 14,500 horses were infected

West Nile virus (2002)

9,862 cases and 264 deaths

Waterborne disease outbreaks

• 28 waterborne disease outbreaks during 2005 and 2006

• 20 were associated with drinking water, 612 infected and four died

• 12 were associated with bacteria [ 135 cases; 4 deaths]

• 3 were associated with viruses [212 cases; no deaths

• 2 were associated with parasites [51 cases; no deaths]

• 1 with combination of bacteria and viruses [139 cases; no deaths]

Foodborne disease outbreaks

• over 200 known diseases can be transmitted through food

• 76 million illnesses, 325,000 hospitalizations, 5,000 deaths per year

• Salmonella and Listeria spp., Campylobacter jejuni, E.coli O157:H7,Toxoplasma, Cyclospora cayetanensis

Ebola VIrus (Sudan)

1976,1979

Ebola Virus (Republic of the Congo)

1976, 1995, 200-2003

Ebola Virus (Gabon)

1994, 1996, 2001-2003)

Ebola Virus (Uganda )

• 2000

• 424 cases, 224 deaths

• Larges Ebola epidemic ever recorded

Spanis Fule Pandemic (1928)

• The most devastating pandemic of the 20th century

• Killed more than 20 million people worldwide, 500,000 in the USA

• Taiwan flu, Hongkong flu, London flue, Port Chamlers flu, Russian flue

HIV AIDS (1959)

• African serum sample collected in 1959, the first documented evidence of HIV infection in humans

• 1979, AIDS epidemic began in United States but 1981, the epidemic detected

• 1983, discovery of virus that causes AIDS

• HIV-1 from chimpanzee, HIV-2 from sooty mangabeys

Tuberculosis Causative Agent

Mycobacterium tuberculosis

TUBERCULOSIS

• The leading cause from a single infectious agent

• ~1.57 million death in 2017 (CDC)

• ~10 million incident TB cases (CDC, 2017)

• 133 cases per 100,000 population (incidence/morbidity rate)

Countries with high incidence of TB

1. INDIA

2. INDONESIA

3. CHINA

4. the PHILIPPINES

5. PAKISTAN

6. NIGERIA

7. BANGLADESH

8. SOUTH AFRICA

Malaria

• the world’s most important tropical parasitic disease

• 3.3 billion people live in malaria-endemic areas

• •.2 billion people live in areas with a high risk of malaria

• Africa has the largest number of people living in areas with high risk of malaria, second, Southeast Asia region

INTERACTIONS AMONG PATHOGENS, HOSTS, and ENVIRONMENTS

Pathogen, Host, Environment = Disease

FACTORS affecting the OCCURRENCE of Infectious Diseases

Susceptible host, router of entry, Infectious agent, reservoir, route of exist, mode of transmission, router of entry

Factors pertaining to the pathogen

• virulence of the pathogen

• a way for the pathogen to enter the body

• the number of organism that enter the body

Factors pertaining to the HOST

• the person’s health status

• the person’s nutritional status

• Susceptibility of the host, socioeconomcial level, occupation, travel, hygiene, substance abuse, immune status

Factors pertaining the environment

• physical factors, geographic location, climate, heat, cold, humidity, and season of the year

• availability of appropriate reservoirs, intermediate host, and vectors

• Sanitary and housing conditions; adequate waste disposal

• availability of potable water

Chaine of infection

• there must be a pathogen

• there must be a source of the pathogen (reservoir)

• there must be a portal of exit

• there must be mode of transmission

• there must be a portal of entry

• there must be susceptible

Strategies for breaking chain of infection (Broad)

• eliminate or contain the reservoirs of pathogens or curtail the persistence of a pathogen at the source

• •prevent contact with infectious substances from exit pathways

• eliminate means of transportation

• block exposure to entry pathways

• reduce or eliminate the susceptibility of potential hosts

Strategies for breaking chain of infection (Specific Methods)

• effective hand hygiene

• good nutrition, rest, and reduced stress

• obtain immunization against common pathogens

• practice insect and rodent control measures

• practice proper patient isolation procedures

• ensure proper decontamination of surfaces and medical instruments

• dispose sharps and infectious waste properly

• use gloves, gowns, mask, respirators, and other PPE

• Use needle safety devices during blood collection

Reservoirs of Infection

• Any site where pathogen can multiply or merely survive until it is transferred to a host

• Living hosts or inanimate objects or materials

Passive Carrier

Carry the pathogen without ever had the disease

Incubatory Carrier

A person who can transmit a pathogen during the incubation period of a particular infectious diseases

Convalescent Carriers

Harbor and can transmit a particular pathogen while recovering from an infectious disease

Active Carriers

Have completely recovered from the disease, but continue to harbor the pathogen indefinitely

Human Carriers

1. Respiratory Secretions

2. Feces

   • Directly from the carrier

   • indirectly through food or water

   • Staphylococcal and streptococcal infections

   • hepatitis, diphtheria, dystenutrt, meningitis, and STDS

Animal Carrier

• Direct contact with animal

• Inhalation or ingestion of the pathogen

• Injections of the pathogen by an anthropod vector

Measures to control zoonotic diseases

• use of personal protective equipment when handling animals

• animal vaccination

• proper use of pesticides

• isolation or destruction of infected animals

• proper disposal of animal carcasses and waste products

Rabies

Transmitted to a human through the saliva that is injected through bites

Toxoplasmosis

Can be contracted by ingesting of oocysts from cat feces present in litter boxes or sand boxes

• present in infected raw/undercooked meats

• cause severe brain damage or death of fetus when contracted by pregnant woman on 1st trimester

Salmonellosis

Diarrheal disease by ingesting Salmonella disease from feces of turtle, reptiles, and poultry

Bovine Spongiform Encephalopathy (Mad Cow Disease)

Acquired by ingestion of prion-infected beef

Anthrax

Contracted from dead animals or animal hides contaminated with the sport of Bacillus anthracis

• inhalation

• ingestion

• through wounds or cuts

Living Reservoirs: Arthropods

• Vectors

• Insects

• Arachnids

Nonliving Reservoirs: Fomites

Inanimate objects capable of transmitting the disease

NONLiving Reservoirs: Health care setting

Patient’s gown, bedding, towels, earring and drinking utensils, bedpans, stethoscopes, latest gloves, electronic thermometers, electrocardiographic electrodes

Direct skin to skin contact

Common cold virus from the hand of someone who just blew his or her nose to another by hand shaking

Direct mucous membrane to mucous membrane contact

• by kissing or sexual intercourse

• STDs: Syphillis, gonorrhea, chlamydia, herpes, HIV

Indirect contact

• Via airborne droplets of respiratory secretions, usually produces as a result of sneezing or coughing

• Colds, influenza, measles, mumps, chickenpox, smallpox, and pneumonia

• via food and water contaminated with fecal matter

Indirect contact via arhopords vectors

mosquitos, flies, fleas, lice, ticks, and mites

Indirect contact via fomites

Respiratory secretions, blood, urine, feces, vomitus, or exudates from hospitalize patients

Indirect contact via transfusion of contaminated blood or blood products

• From an ill person by parenteral injection using non sterile syringes and needles

• Hepatitis, syphilis, Malaria, AIDS, systemic staphylococcal infections

Public Health Agencies

• Strive to prevent epidemics and to identify and eliminate any that do occur

Public Health Agencies help by

• educating the public

• explaining how disease are transmitted

• explaining proper sanitation procedures

• identifying and attempting to eliminate reservoirs of infections

• carrying out measures to isolate diseased persons

• participating in immunization programs

• help to create sick persons

World Health Organization

Specialized agency of UN found in 1948

WHO Missions

• Promote technical cooperation for health among nations

• Carry out programs to control and eradicate diseases

• Improve the quality of human life

Centers for Disease Control and Prevention (CDC)

• Established in 1946 as Communical Disease Center

• Assists state and local health departments in the application of all aspects of epidemiology

CDC Mission

to collaborate to create the expertise, information, and tools that people and communities need to protect their health

Biological Warefare

The use of pathogenic microorganisms to cause harm to others

Biological Warfare Agents

Microbes that are being used in times of war

Clostridium botulinum causes?

Botulism (nerve damage)

Clostridium botulinum

Neurotoxin potential fatal microbial intoxicicatio

Smallpox

fever, malaise, headache, prostration, severe backache

Plague

• Caused by Yersinia pests through flea bite

• bioterrorists could disseminate via aerosols

U.S. Antiterrorism and Effective Death Penalty Act of 1996

• to minimize the danger of potentially microorganisms falling into the wrong hands

• makes the CDC responsible for controlling shipment of select agents to be used as biological weapons

Water

The most essential resource necessary for the survival of humanity

Chemical Pollution

• industrial installations dump into local waters without proper pretreatment

• pesticides are used indiscriminately

• chemical are expelled in the air and carried to earth by rain

Biological Pollution

• fecal material and garbage

• cholera, typhoid fever, bacterial and amebic dysentery, giardiasis, cryptosporidiasis, infectious hepatitis, poliomyelitis