PUBLIC HEALTH ENGINEERING

Health Definitions

What is Health?

  • A state of complete physical, mental, and social well-being, not merely the absence of disease.

  • Defined by the World Health Organization (WHO).

World Health Organization (WHO)

  • The directing and coordinating authority for health within the United Nations system.

What is Public Health?

  • Organized measures to prevent disease, promote health, and prolong life among the population.

  • Focuses on entire populations, not individual patients or diseases.

  • Aims to provide conditions in which people can be healthy (WHO).

What is Environmental Health?

  • Branch of Public Health concerned with the natural and built environment that may affect human health.

  • Focuses on aspects of human health and disease determined by environmental factors.

  • Involves assessing and controlling environmental factors that can potentially affect health (WHO).

  • The total relationship of humans to their physical, biological, socio-economic, and socio-cultural environment as it affects well-being.

What is Environmental Sanitation?

  • Science dealing with the prevention and control of diseases by eliminating or controlling environmental factors in disease transmission.

  • Control of all factors in man's physical environment that significantly affect physical development, health, and survival.

What is Engineering?

  • Application of mathematical and natural sciences, gained by study, experience, and practice, with judgment, to economically utilize materials and forces of nature for mankind's benefit. (Defined by the Accreditation Board for Engineering and Technology)

What is Public Health Engineering?

  • Deals with the control of the environment through modifications, protective, and preventive measures.

  • Aims at providing optimum conditions for health and well-being.

What is Disease?

  • A particular abnormal condition negatively affecting the structure or function of an organism, not due to immediate external injury.

  • According to Dorland's Medical Dictionary, it is any harmful deviation from the normal structural or functional state, associated with signs and symptoms, and differing in nature from physical injury.

  • Britannica defines it as a disorder of structure or function in a human, animal, or plant, producing specific signs or symptoms, affecting a specific location, and not a direct result of physical injury.

  • Oxford defines it simply as the opposite of health.

Study of Disease

Pathology

  • The study of the essential nature of diseases and the structural and functional changes they produce.

Epidemiology

  • The study of the distribution of a disease or condition in a population.

  • Science dealing with the inter-relationship of factors and conditions determining the frequencies and distributions of an infectious process, a disease, or a physical state in a human community.

  • Study of the occurrence of a disease in populations.

  • Concerned with the series of events that makes a disease possible.

  • Provides prevention and control measures based on scientific principles and procedures.

  • Concerned with the disease process and ways of controlling the disease.

  • Studies the major forces involved in the infectious process: person or host, agent, and environment.

Disease Classification

Congenital

  • Present at birth.

Acquired

  • Began at some point during one's lifetime.

Communicable

  • Can pass from person to person.

Contagious

  • Can easily pass from person to person by direct contact.

Non-communicable

  • Not passed from person to person.

Degenerative

  • Due to malfunctioning of vital body organs over time.

Deficiency (Nutritional)

  • Due to lack of essential nutrients in diet.

Allergies

  • Due to hypersensitivity of the body to certain foreign substances.

Cancer

  • Due to uncontrolled growth of cells/tissues.

Mental

  • Emotional or psychosomatic.

Acute, Chronic, and Other Disease Descriptions

Acute

  • Disease in which symptoms develop rapidly and that runs its course quickly.

Chronic

  • Disease with usually mild symptoms that develop slowly and last a long time.

Subacute

  • Disease with time course and symptoms between acute and chronic.

Asymptomatic

  • Disease without symptoms.

Latent

  • Disease that appears a long time after infection.

Local Infection

  • Infection confined to a small region of body.

Systematic Infection

  • Widespread infection in many systems of the body.

Focal Infection

  • Infection that serves as a source of pathogens for infection at other sites in the body.

Primary Infection

  • Initial infection within a given patient.

Secondary Infection

  • Infections that follow a primary infection, often by opportunistic pathogens.

Types of disease transmission

Genetic

  • Caused by one or more genetic mutations.

Hereditary

  • Errors in genetic code received from parents.

Hormonal (Endocrine)

  • Excess or deficiency of hormone.

Immunological

  • Hyperactive or hypoactive immunity.

Neoplastic

  • Abnormal cell growth.

Iatrogenic

  • Caused by medical treatment/procedure.

Idiopathic

  • Unknown cause or source.

Natural History of Disease

Prepathogenesis Phase

  • Phase before a disease infects an individual through interaction of the agent, the host, and the environment factors.

Concept of Disease Occurrence

  • Result of an interaction of three factors: Host, Agent, and Environment.

    • Infectious agent - is a microorganism capable of producing infectious disease under circumstances of host and environment favoring transmission.

      • Infectivity - ability of an infectious agent to cause infection

      • Pathogenicity - ability of an agent to cause disease after infection

      • Virulence - ability of an infectious agent to cause severe disease

    • Host - is a person or other living organism that can be infected by an infectious agent under natural conditions.

      • Opportunities for exposure

      • Susceptibility and response

    • Environment - refers to the ecological conditions that favor the interaction of host and agent e.g. swampy areas, bushes within households, sanitation etc.

      • Physical factor (geology and climate)

      • Biologic factors (insects)

      • Socioeconomic factors (crowding, sanitation, and the availability of health services)

Pathogenesis Phase

  • When the agent becomes established in the host.

  • Start of the four periods of infectious disease.

Four Periods of Infectious Disease

  • Incubation period: Time that elapses between arrival of the pathogen and onset of symptoms.

  • Prodromal period: Time during which the patient feels "out of sorts" but is not yet experiencing actual symptoms of the disease.

  • Period of Illness: Time during which the patient experiences the typical symptoms associated with that particular disease.

  • Convalescent period: Time during which the patient recovers.

Chain of Infection

  • The infection process can be described as a chain composed of links which are clasped securely to one another from beginning to end.

Infectious Agent

  • Infectious agents: Organisms capable of spreading disease.

  • Pathogens: Organisms that cause disease.

  • Examples:

    • Bacteria

    • Viruses

    • Fungi

    • Protozoa

    • Helminths

    • Chemical Contaminants

Incubation Periods for Various Diseases:

  • Chickenpox: 14-16 days

  • Cholera: 1-3 days

  • Diphtheria: 2-6 days

  • Gas gangrene: 1-5 days

  • Gonorrhea: 3-5 days

  • Hepatitis A: 2 weeks-2 months

  • Hepatitis B: 6 weeks-6 months

  • Hepatitis C: 2 weeks-6 months

  • Herpes simplex: 4 days

  • Influenza: 1-3 days

  • Leprosy: 3 months-20+ years

  • Measles: 10-12 days

  • Meningitis (bacterial): 1-7 days

  • Mumps: 2-3 weeks

  • Pertussis: 5 days-3 weeks

  • Pinworm: 2-6 weeks

  • Plague: 2-6 days

  • Polio: 7-14 days

  • Rabies: 2 weeks-2 months (up to 1 year)

  • Salmonella food poisoning: 12-72 hours

  • Staphylococcus food poisoning: 1-8 hours

  • Syphilis: 10 days-3 months

  • Tetanus: 3 days-5 weeks

  • Tuberculosis: 2-10 weeks

Reservoirs of Infection

  • The habitat in which an infectious agent normally lives, grows and multiplies or merely survives until it is transferred to a host.

  • Living reservoirs (human and animal reservoirs)

  • Non-living/Environmental reservoirs (materials and inanimate objects).

Human as Reservoir

  • Intestine, Mouth, Nose, Throat, Respiratory tract, Skin

  • Colonization - when bacteria are present in a person's nose, mouth, gut or other site, but do not cause illness.

  • Normal microbiota or indigenous microbiota

    • Resident microbiota

    • Transient microbiota


  • SKIN

    • Resident microbes:

      • Staphylococcus (especially epidermidis)

      • Proprionibacterium (especially acnes)

      • Micrococcus

      • Corynebacterium (diphtheroids)

    • Transient microbes:

      • Staphylococcus aureus

      • Clostridium (especially perfringens)

      • Bacillus

  • EYES

    • Staphylococcus sp. (coagulase-negative)

    • Streptococcus sp. (α\alpha-hemolytic)

    • Neisseria sp.

    • Haemophilus sp.

  • EARS

    • Staphylococcus sp. (coagulase-negative)

    • Streptococcus pneumonia

    • Pseudomonas aeruginosa

    • Enterobacteriaceae


  • UPPER RESPIRATORY TRACT

    • Nares

      • Staphylococcus aureus

Nasopharynx and Oropharynx:

  • Staphylococcus sp.

  • Micrococcus sp.

  • Streptococcus sp. (α\alpha- and β\beta-hemolytic)

  • Peptostreptococcus

  • Enterococcus

  • Neisseria sp.

  • Haemophilus

  • Moraxelia

  • Mycoplasma

  • Corynebacterium (diptheroids)

  • Enterobacteriaceae

  • Pseudomonas aeruginosa


  • MOUTH

    • Streptococcus sp. (α- and β-hemolytic)

    • viridans streptococci (especially Streptococcus mutans)

    • Neisseria sp.

    • diphtheroids (Corynebacterium)

    • Staphylococcus aureus

    • Staphylococcus epidermidis

    • Lactobacillus sp.

    • Mycoplasma

  • Gums

    • Bacteroides

    • Fusobacterium

    • Clostridium

    • Peptostreptococcus

  • LARGE INTESTINE/COLON

    • Bifidobacterium

    • Eubacterium

    • Bacteroides

    • Fusobacterium

    • Clostridium

    • Lactobacillus

    • Enterococcus

    • Enterobacteriaceae

  • Carrier

    • A person or animal without apparent disease who harbors a specific infectious agent and is capable of transmitting the agent to others.

      • Types of Carrier

        • Passive carriers - carry the pathogen without ever having the disease.

        • Incubatory carrier - is a person who is capable of transmitting a pathogen during the incubatory period of a particular infectious disease.

        • Convalescent carriers - harbor and can transmit pathogen while recovering from an infectious disease.

        • Active carriers - have completely recovered from the disease but continue to harbor the pathogen indefinitely.

        • The carrier state may be of short duration (Transient carrier) or long duration (Chronic carrier).

Animals as Reservoir

  • Rabies (dogs, bats, skunks, foxes)

  • Yellow Fever (monkeys)

  • Plague (rodents)

  • Lyme Disease (deer)

  • Brucellosis (cows and pigs)

  • Anthrax (sheep)

  • Trichinellosis/Trichinosis (swine)

  • Tularemia (rabbits)

  • West Nile Encephalitis (birds)

Zoonotic Diseases (Zoonosis)

  • An infection or an infectious disease of animals transmissible under natural conditions to man.

Arthropods

  • Invertebrates (without back bones) with joined legs and commonly associated with human infections, including insects and spiders.

  • Examples are mosquitoes, biting flies, lice, fleas, and arachnids.

  • When involved in transmission of diseases, these arthropods are called Vectors.

Asymptomatic infections

  • Bacillary dysentery

    • common

  • Cholera (El Tor)

    • only 1 in 30-50 infections develops illness

  • Giardiasis

    • 1 in 2-4 infections develops illness

  • Polio

    • only 1 in 1,000 infections develops illness

  • Typhoid fever

    • very common

  • Schistosomiasis

    • very common

  • Hookworm

    • very common

  • Yellow fever

    • common

  • Japanese Encephalitis

    • common

  • Filariasis

    • common during epidemics

  • Malaria

    • very common

  • River blindness

    • very common

  • Plague

    • very common

Environmental/Nonliving Reservoir

  • Includes air, plants, soil, dust, food milk, water, and fomites.

  • Fomites are inanimate objects capable of transmitting pathogens.

    • Healthcare: patient's gowns, bedding, towels, eating and drinking utensils, and hospital equipment.

    • Telephones, doorknobs, and computer keyboards can serve as fomites.

Portals of Exit

  • The most frequent portals of exit in man are:

    • Skin through open lesions or with the aid of insects or hypodermic needles.

    • Respiratory tract

    • Gastrointestinal tract

    • Eyes / Ears

Modes of Transmission

  • Principal modes

    • Direct Transmission

      • Direct Contact. The immediate transfer of an agent from a reservoir to a susceptible host by direct physical contact.

      • Droplet Transmission. Involves the transfer of pathogens via infectious droplets. Droplets may be generated by coughing, sneezing, and even talking.

    • Indirect Transmission

      • The transmission of an agent carried from a reservoir to a susceptible host by suspended air particles, inanimate objects (vehicles or fomites), or animate intermediaries (vectors).

        • Airborne Transmission - Involves the dispersal of droplet nuclei, which are residue of evaporated droplets.

        • Vehicleborne Transmission. Indirectly transmit an infectious agent include food, water, biologic products (blood), and fomites.

          • Fomites - Inanimate objects that have come in contact with a sick person.

Vector

  • Mosquito

    • Aedes

      • Chikungunya, Virus

      • Dengue, Virus

      • Lymphatic filariasis, Parasite

      • Rift Valley fever, Virus

      • Yellow Fever, Virus

      • Zika, Virus

    • Anopheles

      • Lymphatic filariasis, Parasite

      • Malaria, Parasite

    • Culex

      • Japanese encephalitis, Virus

      • Lymphatic filariasis, Parasite

      • West Nile fever, Virus

  • Aquatic snails

    • Schistosomiasis (bilharziasis), Parasite

  • Blackflies

    • Onchocerciasis (river blindness), Parasite

  • Fleas

    • Plague (transmitted from rats to humans), Bacteria

    • Tungiasis, Ectoparasite

  • Lice

    • Typhus, Bacteria

    • Louse-borne relapsing fever, Bacteria

  • Sandflies

    • Leishmaniasis, Parasite

    • Sandfly fever (phlebotomus fever), Virus

  • Ticks

    • Crimean-Congo haemorrhagic fever, Virus

    • Lyme disease, Bacteria

    • Relapsing fever (borreliosis), Bacteria

    • Rickettsial diseases (eg, spotted fever and Q fever), Bacteria

    • Tick-borne encephalitis, Virus

    • Tularaemia, Bacteria

  • Triatome bugs

    • Chagas disease (American trypanosomiasis), Parasite

  • Tsetse flies

    • Sleeping sickness (African trypanosomiasis), Parasite

Vector Transmission

  • Involves the various types of biting insects and arachnids.

    • Biological Vector

      • Mosquitoes

      • Ticks

      • Flea

      • Louse

      • Bloodsucking flies

      • Bloodsucking bug

      • Mite

    • Mechanical Vector

      • Housefly

      • Cockroaches

Portals of Entry

  • The manner of entry are similar with the mode of exit from the reservoir.

  • The most important portals of entry are:

    • Skin

    • Mucous membranes

      • Respiratory

      • Gastrointestinal

      • Urinary

      • Reproductive

      • Conjunctiva

    • Placenta

  • Pathogens that cross the placenta

    • Taxoplasmosis

    • Syphilis

    • Listeriosis

    • AIDS

    • German measles

  • Channels of infection are means through which the body becomes infected by disease-producing agents. The channels may be the respiratory tract, the digestive tract, exterior surfaces of the body.

Host Defense Mechanism

  • Nonspecific

    • First Line of Defense

      • Intact skin and mucous membrane

      • Dryness, acidity, temperature of skin, perspiration

      • Digestive enzymes

      • Peristalsis and urination

      • Indigenous microflora

    • Second Line of Defense

      • Cellular and chemical responses

      • Production of fever, production of interferons, activation of the complement system, inflammation, chemotaxis, and phagocytosis

  • Specific

    • Third Line of Defense

      • Immune system

Level of Disease Transmission

Sporadic

  • Implies the occurrence of a few scattered cases of the disease without relationship to other cases; a few cases every now and then.

  • Disease that occurs only occasionally within the population of a particular geographic area.

Endemic

  • Is the term applied to a specific disease when it normally prevails in a locality and does not fluctuate markedly from the normal expected incidence in the community.

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

Hyperendemic

  • Refers to persistent, high levels of disease occurrence

Epidemic

  • Is the incidence of a communicable disease among a number of people to an extent that is recognized statistically as being well beyond the normal expectancy for the disease in a community in a definite period of time.

  • Greater than usual number of cases of a disease in a particular region, usually occurring within a relatively short period of time.

  • Outbreak - carries the same definition of epidemic, but is often used for a more limited geographic area

Pandemic

  • Affects large number of people at the same time and transcends community boundaries.

  • Disease that is occurring in epidemic proportions in many countries simultaneously - sometimes worldwide.

Three Levels of Disease Prevention

Primary prevention

  • Refers to the measure that may be applied in the prepathogenesis phase of the natural history of disease.

  • Intervening before health effects occur, through measures such as vaccinations, altering risky behaviors such as poor eating habits, tobacco use, etc., and banning substances known to be associated with a disease or health condition (CDC)

  • Health Promotion - The process of enabling people to increase control over, and to improve health (WHO)

  • Specific Protection

Secondary prevention

  • This is applied in the early pathogenesis phase. This consists of early diagnosis and prompt treatment of the disease in order to arrest the disease and prevent its spread to other people.

  • screening to identify diseases in the earliest stages, before the onset of signs and symptoms, through measures such as mammography and regular blood pressure testing (CDC)

Tertiary prevention

  • includes disability limitation and rehabilitation.