Transcript Epidemiology and Public Health

Epidemiology and Public Health
(Two Lectures)
BY
Prof. DR. Zainalabideen A. Abdulla,
DTM&H., MRCPI, Ph.D., FRCPath. (U.K.)
Learning Objectives
Epidemiology
Is the study of factors that determine the
frequency, distribution, and determinants of
diseases in human populations.
- Microbiology & infectious diseases
- Terminology
- John Snow is the father of epidemiology
(conducted a study in London about Cholera
transmission; end of 19th century)
Infectious disease: Caused by a pathogen
Communicable disease: Transmissible
(person TO person)
e.g. Gonorrhea
Contagious disease: Easily transmitted
e.g. Influenza
Zoonotic diseases (zoonosis):
Animal
Humans
Incidence
Number of NEW cases of a disease in a defined
population during a specific time period
Morbidity : The same, but per a specifically
defined population (e.g. 1,000, 10,000, 100,000)
Prevalence
Period Prevalence: Total number of cases in a
given population during specific time period (e.g.
in 2012)
Point prevalence: The same but in a particular
moment (e.g. now)
Mortality Rate (Death Rate)
Number of deaths of a particular disease during
a specific time period per a specified population
(per 1,000, 10,000, 100,000)
Sporadic Diseases
Diseases occur occasionally within a population
of a particular area, e.g. Cholera in USA
Endemic diseases
Always present within the population of a
particular area, e.g. tuberculosis in USA
Epidemic Diseases
A greater than usual number of cases of a
disease in a particular region occurring within a
relatively short period of time, e.g. fungal
meningitis in 2012 in USA.
Waterborne disease outbreaks
From drinking (e.g. bacteria, viruses, parasites)
or recreational (e.g. Cryptosporidium) water
Foodborne disease outbreaks
Norovirus most common in USA
Pandemic Disease
A disease occurring in epidemic proportions in
many countries simultaneously/worldwide, e.g.
Spanish flu in 20th century (killed 20 millions)
Most Common Pandemic Diseases
• HIV/AIDS
• Tuberculosis
• Malaria
- > 300 million; > 5 million deaths
HIV/AIDS
- Epidemic started 1979 (recorded 1981) in USA
• Now > 1 million with HIV in USA)
• Worldwide: 35 million
- HIV1 and HIV2 viruses
- 10-15 years to develop after HIV infection
- Different modes of transmission
Tuberculosis
• Multidrug-resistant tuberculosis (MDR-TB)
Extensively drug-resistant tuberculosis (XDR-TB)
• Second killer after HIV/AIDS.
• 1/3 of the world population infected with TB
(Latent TB)
• Leading killer of AIDS patients
Malaria
• 5th leading cause of death worldwide (RTI,
HIV/AIDS, diarrhea, TB)
• Most common in sub-Saharan Africa
• Half world’s population at risk
• > ½ million deaths worldwide; every 1 minute 1
child die in Africa (second leading cause of
death after AIDS)
Interaction: pathogens, hosts & environment
I. Pathogens
• Virulence
• Portal of entry
• Numbers
II. Host
• Health status
• Nutritional status
• Susceptibility
cont./…
cont./…Interactions
IIII. Environment:
• Physical factors
• Reservoirs
• Sanitary/housing
Infectious disease
Virulence X Numbers vs Host Factors
Chain of Infection
1. Pathogen
2. Reservoir
3. Portal of exit
4. Mode of transmission
5. Portal of entry
6. Susceptible host
Strategies of breaking the chain of infection
Broad goals:
• Eliminate/contain Reservoir
• Prevent contact with Exit
• Eliminate transmission
• Block entry
• Reduce/eliminate susceptibility
cont./…
cont./… Strategies of breaking chain
Specific methods:
• Hand hygiene
• Good nutrition
• Immunization
• Insect/rodent control
• Patient isolation
• Decontamination
• Wastes disposal
• Sanitation and safety measures
Reservoirs of infections
Is any site where the pathogen can multiply or
survive until transferred to a host.
Reservoirs: • Living hosts
• Inanimate objects
Human carriers
• Other humans (patients or carriers)
• Carrier = With pathogens, but no disease:
- Passive: Never had the disease
- Incubatory: Transfer disease during I.P.
- Convalescent: Transfer disease during
recovery period
- Active: Completely recovered, continue
to harbor the pathogen indefinitely
(e.g. Mary Mallon: Typhoid Mary)
Animals
Zoonotic diseases: Humans acquired them
from animal sources via direct contact,
inhalation, ingestion, or injection by arthropod.
Examples (Table):
. Rabies
. Toxoplasmosis
. Salmonellosis
. Variant CJ disease
. Anthrax (B. anthracis)
. Brucellosis, Campylobacteriosis
Arthropods (vectors)
. Insects (e.g. mosquitoes, lice, fleas, flies)
. Arachnids (e.g. mites, ticks)
Blood (pathogen)
- Table/Figure
Healthy Individual
e.g. Malaria
Nonliving reservoirs
• Air, soil, dust, food, milk, water and fomites
• Air contaminated by human secretions: Talk,
breathing, sneezing, and coughing; or via air
vents/current
• Most contagious: Colds and Influenza
• Dust: Carry bacteria and spores, fungi- dried
cont./…
cont./… nonliving reservoirs
• Soil: Spores (e.g. Clostridium: tetanus,
botulism, gas gangrene)
• Food & Milk: Pathogens
Food poisoning
(Dirty hands, soil, dust, hair, secretions, etc)
Examples: Amebiasis, Cholera, hepatitis A
• Fomites: Gowns, towels, utensils, equipment
contaminated by RT, GIT, skin)
• Dust: Carry bacteria and spores, fungi- dried
Modes of transmission
• Contact, Droplet, Airborne, Vehicular, Vector
Droplets: • 5 µm or more in diameter
• Coughing, sneezing, talking
Airborne: • Dispersal of droplet nuclei (residue
of evaporated droplets)
• < 5 µm
Vehicular: Food, water, dusts, fomites
- Contact (direct & indirect); Vector: Discussed
Communicable diseases
Infectious diseases transmitted from person to
persons via:
1. Direct skin-to-skin contact
• Common cold virus- by hands shaking
• Healthcare workers: Wash hands
2. Direct mm-to-mm by kissing/sexual contact
• Most STD (Chlamydia “ most common
notifiable disease in USA”, syphilis,
gonorrhea, HIV, and herpes virus)
cont./…
cont./… communicable diseases transmission
3. Indirect contact via airborne droplets of
respiratory secretions, usually produced as a
result of sneezing or coughing:
• Most contagious airborne diseases
• Pathogens carried by dust
• Colds, influenza, measles, mumps,
chickenpox, smallpox, pneumonia
cont./… communicable diseases transmission
3. Indirect contact via food and water
contamination with fecal material
• Restaurant food handlers
4. Indirect contact via arthropod vectors
5. Indirect contact via fomites that become
contaminated by respiratory secretions, blood,
urine, feces, vomitus, or exudates from
hospitalized patients
• Table
cont./…
cont./… communicable diseases transmission
6. Indirect contact via transfusion of
contaminated blood or blood products from an ill
person or by parenteral injection (injection
directly into the blood-stream) using nonsterile
syringes and needles, so:
• Disposable materials used in hospitals
Public Health Agencies
1. World Health Organization (WHO)
• Founded in 1948
• Epidemiological terms regarding
an infectious disease (Table):
- Control
- Elimination
- Eradication
cont./…
cont./… public health agencies
2. The Centers for Disease Control and
Prevention (CDC):
. USA, founded in 1946
. Aspects of epidemiology/microbiology
. Notifiable diseases should be reported
. Table: ¾ top- are sexually transmitted,
2/10 are vaccine-preventable
Bioterrorism and Biological Warfare Agents
Anthrax
• Cause: B. anthracis /G+, spore-forming B
• Forms: Inhalation, GI, cutaneous (Eschar)
“according to severity”
• Involve: Hemorrhage, serous effusion
• Spread/spores: Aerosols, food, mail
• Prevention: Antibiotic therapy
Botulism
• Cause: Clostridium botulinum Toxin
(neurotoxin)/ G+ spore-forming bacilli
• Nerve damage, visual difficulty, respiratory
failure, flaccid paralysis, brain damage, death
• Source: Toxin to water supply, food, or
spores into open wounds
Smallpox
• Serious, contagious
fatal
• Fever, malaise, headache, prostration,
severe backache, skin rash
bleeding
into skin and mm
• WHO: 1980 eradicated
No need for
vaccination
• Preserved virus
Risk to wrong hands
Plaque (Black Death)
• Cause: Yersinia pestis/ G- coccobacilli
• Zoonosis, transmitted by flea bites
• Types: Bubonic, septicemic, pneumonic,
and meningitis
• Transmission: Aerosols, person-to-person
Bubonic: Swollen, inflamed, tender L.N. (buboes)
Pneumonic: Highly communicable/lungs
Septicemic: Cause septic shock and meningitis
Water supply pollution
1. Chemical
2. Biological
Sources
• Rainwater falling
• Sewage into rivers
• Shallow water vs deep wells
• Cracked water pipes
Water treatment
• Filter
• Sedimentation or settling
• Coagulation/flocculation: Alum (Aluminum K Sulfate)
• Sand filter (remove organisms)
• Membrane filters (Tiny cysts: Giardia lamblia,
Cryptosporidium 4-6 µm)
• Check contamination (fecal- Coliforms): E. coli,
Enterobacter, Klebsiella:
Safe = 1 coliform /100 ml water or less
Common: G. lamblia, Cryptosporidium, E. coli
O157:H7, Shigella, and norovirus
Boiling 20 min kill tiny organisms, not spores or viruses
Sewage treatment
Primary sewage
Filter (screening), skimmer removed, settle,
flocculation
Primary sludge
Secondary sewage: Primary effluent
Aeration and trickling (aerobic microbes break
organic into CO2 & H2O)
settle
Secondary effluent
filter/chlorinated
River
Tertiary Sewage
To drinking water, expensive, need to treat