Air Borne Infection:Epidemiology and control measures

Moderator: Prof.A.M.Mehendale

Presenter : Dr.Rohan

Defination

Epidemiology is the study of the distribution and determinants of health-related states or events (including disease), and the application of this study to the control of

diseases and other health problems ’

- John M.

Last(1988)

Communicable Diseases:

A communicable (or infectious) disease is one caused by transmission of a specific pathogenic agent to a susceptible host.

• Directly, from other infected humans or animals, or• Indirectly, through vectors, airborne particles or vehicles.

Theories of Disease Causation

Theory of humors (humor means fluid): The miasmatic theory of disease Theory of contagion Germ theory Koch’s postulates

Epidemiological triad

Epidemiological triad r

Agent Factors Physical Agents Chemical Agents Biological Agents Nutritional agents Host Factors

Socio-demographic Factors Psycho-social Factors Intrinsic Characteristics

Environmental FactorsPhysical Environment Biological Environment Social Environment

Impact of communicable Diseases Six causes account for almost half of all

premature deaths, mostly in children and young adults, and account for almost 80% of all deaths from infectious diseases:

  Acute respiratory infections (3.76 million) HIV/AIDS (2.8 million) Diarrhoeal diseases (1.7 million) Tuberculosis (1.6 million) Malaria (1 million) Measles (0.8 million) 

Definitions

Epidemic

Epidemics are defined as the occurrence of cases in excess of what is normally expected in a community or region.

Epidemic varies according agent, the size, type susceptibility of population exposed, and the time and place of occurrence.

Agent

‘A substance, living or non living, or a force, tangible or intangible, the excessive presence or relative lack of which may initiate or perpetuate a disease process’

Biological Nutrient Physical Chemical Mechanical Social

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The pathogenicity of the agent: its ability to produce disease, measured by the ratio of the number of persons developing clinical illness to the number exposed.

Virulence: a measure of the severity of disease, which can vary from very low to very high.

Infective dose: the amount required to cause infection in susceptible subjects.

The source of infection: the person or object from which the host acquires the agent.

Host

‘the person or animal that provides a suitable place for an infectious agent to grow and multiply under natural conditions’

Intrinsic Demographic characteristicsBiological characteristicsSocio-economicLifestyle characteristics

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The incubation period—the time between entry of the infectious agent and the appearance of the first sign or symptom of the disease.

Environment (Extrinsic) Physical Enviornment Bilogical Environment Psychosocial Enviornment

Air Borne Disease:

“A mechanism of transmission of an infectious agent by particles, dust or droplet nuclei suspended in air”

Two types of particles are implicated the airborne form of spread of infectious agent

o Droplet Nucleio Droplet Particles

Droplet Nuclei

tiny particles (1-10 microns) that represent the dried residue of droplets. Smaller particles (<3 microns) in diameter may

contain one or two micro-organism which fail to settle due to gravity and

remain suspended in the atmosphere for long periods of time.

Dust

Larger droplets which are expelled during talking, coughing or sneezing, settle down by their sheer weight on the floor and other objects in the immediate environment.

streptococci, viruses and fungal spores and skin squmae have been found in the dust.

Some of them as TB bacilli may remain viable under optimum condition of temperature and moisture.

Dust released becomes infective again. This type of transmission is more common in hospital settings.

Fig.Partticle size and presence of particulate matters with settling velocity 

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Agent Factors:Main agent in Air borne infection are viruses, bacterias or Fungal spores

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Viruses bacterias Fungi

Herpes Simplex virus 3 (chickenpox)

Corynebacterium diphtheriae Coccidomycosis

Paramyxovirus(Measles) Bacilli Pertussis Other Agents

Togavirus(Rubella) Mycobacterium Tuberculosis

Myxovirus(Mumps) Meningococcal Meningitis Chlamydia typeB (Psittacosis)

Orthomyxovirus (Influenza) Streptococcal Pneumoniae Coxiella Burnetti(Q fever)

Respiratiory Syncitial Virus Staphyalococcal Pyogens Mycoplasma Pneumoniae

Rhinovirus Bacilli Anthracic( Anthrax)

Source Of Infection: Either clinical, Subclinical case or carriers

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Infections caused by clinical case:•Chicken pox•Measles•Rubella•Mumps (no sub-clinical case)•Influenza•Diphtheria•Pertussis (no sub-clinical case)•Mycobacterim TB

Carrier:•Diphetheria (95%)•Meningococcal Meningitis(70-80%)•Mycobacterium TB

Incubation Period:

All the viral infections have short incubation period varying from 1-3weeks.

Shortest incubation period is for influenza which is 18 to 72 hours.In case of Bacterial infections incubation period is as:Diphtheria 2-6 daysPertussis (no sub-clinical case) 7-14 daysMeningococcal Meningitis 2-10 days

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Period of communicability:Highly infectious in early stage of disease (Prodromal Period)

Secondary attack Rate:

Secondary attack rate is highest in case of Chickenpox 90% and Mumps 86%.In case of bacterial infection if person is unimmunized it may range to 90% (Pertussis)

All viral infections confers lifelong immunity (once attacked)

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Infective material: Nasopharyngeal, Bronchial secretions or skin

squmae can also be source of infection.

Host Factors: Age: Most susceptible age group is 6months-3 yrs

more common in less than 5yrs of age and elderly people except influenza which is common in all ages.

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Sex:

Both the sexes are equally susceptible

Genetic: Twin studies have shown that monozygotic twins are more prone to infection than dizygotic ones.

  Blood Groups:

Analyzing on the basis of ABO typing of blood groups it’s been seen that AB and B blood group people are susceptible than A and O blood group. 

Nutrition:

Malnutrition favors the infection and subsequent spread of disease.

 

Stress:Some studies have shown that stress may reduce cell mediated immunity and a factor responsible for air borne infection. Occupation:People working in the mines, silica industry are more prone to air borne infection. People working in the health care setting are more exposed to air borne infectious agents.  

Human mobility: Infections are more common in people who are generally mobile on duty.

Environmental Factors:

Air borne infection is more common in the winter and spring region.

In India Influenza infection is more common in the summer season.

Diphtheria, Measles are common in all the season.

Winter season favors the transmission due to dampness and humidity.

 

Overcrowding: favors the transmission of the air borne infection. Eg: schools, barracks, and railway platform etc. attack rates are high in close population.  Ventilation:Poor ventilation refers to absence of clean air which increases the potential of air borne infection. Light:An ultraviolet ray of sunlight kills antimicrobials in the air

and renders it clean and keep non humid environment. 

Environmental Factors

The following factors have been associated with the emergence and spread of infectious diseases

the changes in human demographics and behaviour the impact of new technologies and industries economic development and changes in land use increased international travel and commerce microbial adaptation and change the breakdown of public health measures, and Sharing an environment with domestic or wild

animals or birds

Mechanism of Air Borne Infection:

Air Borne infection Control

Early RecognitionRapid identification of Patients Prone of air borne

Diseases: Clinical indications: Unexplained cough

Severe acute febrile respiratory illness (e.g., fever > 38°C, cough, shortness of breath)

Exposure history consistent with ARD of potential concern

Epidemiological indications History of travel to area affected by ARDs Possible occupational exposure Unprotected contact with ARDs patient(s)

Standard Precautions

• Hand hygiene

• Respiratory hygiene/cough etiquette

• Use of personal protective equipment (PPE)

• Prevention of needle sticks/sharps injuries

• Cleaning and disinfection of the environment

and equipment

Hand Hygiene Hand hygiene should be performed:

before and after any direct contact with a patient

after contact with blood, body fluids, secretions and excretions

after contact with items contaminated with blood, body fluids, secretions and excretions, including respiratory secretions

Use alcohol-based hand rub or wash hands with soap and water Wash hands if visibly soiled

Respiratory Hygiene/Cough Etiquette

Droplet Precautions Protection against respiratory pathogens

transmitted by large droplets

In addition to Standard Precautions: Use a medical mask when < 1 m of patient Maintain a distance ≥ 1 meter between

infectious patient and others Place patient in a single room or cohort with

similar patients Limit movement

•Isolation/separation•Masks•Effective treatment

Administrative controls

EnvironmentalControls

Dilution (ventilation)Removal (Fans)Decontamination (UVGI)

Respiratory Protectio

AIRBORNE PRECAUTIONS Private room with monitored negative air pressure 6-12 air changes per hour High efficiency particulate air (HEPA) filtration for

recirculated air HCWs wear respirators (minimum N95) Limit patient movement/transport

AIRBORNE PRECAUTIONSDisease Room Mask/Respirator

Immnune Non Immune

Vericella/Disseminated AIIR None Mask

Measles AIIR None Mask

Tuberculosis AIIR NA Respirator

SARS AIIR NA Respirator

Novel Flu AIIR NA Respirator

Personal Protective Equipment Types of PPE Used in Healthcare Settings

Gloves – protect hands

Gowns/aprons – protect skin and/or clothing

Masks and respirators– protect mouth/nose– Respirators – protect respiratory tract from

airborne infectious agents

Goggles – protect eyes

Face shields – protect face, mouth, nose, and eyes

PPE for Standard Precautions: Based on Risk Assessment

IF direct contact with blood & body fluids, secretions, excretions, mucous membranes, non-intact skin Gloves Gown

IF there is the risk of spills onto the body and/or face Gloves Gown Face protection (mask plus eye protection

goggle or visor; face shield)

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Contact Precautions Gloves Gown

Droplet Precautions Medical mask

Airborne Precautions Particulate respirator

References:

1. Last JM. A Dictionary of medical epidemiology, 4th edition.

2. Langmuir A. D. (1961). "Epidemiology of airborne infection." Bacteriology Reviews 25: 173-181.

  3. Hill AB. The environment and disease: association or causation? Proc R

Soc Med 1965;58: 295-300.

4. Nelson KE, Williams C. Infectious Disease Epidemiology: Theory and practice;(1): 483-496.

Christie AB. Infectious diseases vol.1 & 2 ;(4): 898-1022.

5. R. Bonita, R. Beaglehole, T. Kjellström. Basic epidemiology / 2nd edition. Epidemiology. World Health Organization

6. Infection prevention and control of epidemic- and pandemic-prone acute respiratory diseases in health care WHO Interim Guidelines, 2007.