Air Borne Infection:
Epidemiology and control measures
Moderator: Prof.A.M.Mehendale
Presenter : Dr.Rohan
Defination
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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.
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Directly, from other infected humans or animals, or
Indirectly, through vectors, airborne particles or vehicles.
Theories of Disease Causation
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Theory of humors (humor means fluid):
The miasmatic theory of disease
Theory of contagion
Germ theory
Koch’s postulates
Epidemiological triad
Epidemiological triad
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Agent Factors
Physical Agents
Chemical Agents
Biological Agents
Nutritional agents
Environmental Factors
Physical Environment
Biological Environment
Social Environment
Host Factors
Socio-demographic Factors
Psycho-social Factors
Intrinsic Characteristics
Impact of communicable Diseases
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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)
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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 characteristics
Biological characteristics
Socio-economic
Lifestyle 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
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Droplet Nuclei
Droplet Particles
Droplet Nuclei
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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
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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
Viruses
bacterias
Fungi
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Herpes Simplex
virus 3 (chickenpox)
Corynebacterium diphtheriae
Coccidomycosis
Paramyxovirus(Measles)
Bacilli Pertussis
Other Agents
Togavirus(Rubella)
Mycobacterium Tuberculosis
Myxovirus(Mumps)
Meningococcal Meningitis
Chlamydia
(Psittacosis)
Orthomyxovirus (Influenza)
Streptococcal Pneumoniae
Coxiella Burnetti
(Q fever)
Respiratiory Syncitial Virus
Staphyalococcal Pyogens
Mycoplasma
Pneumoniae
Rhinovirus
Bacilli Anthracic( Anthrax)
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typeB
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:
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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 days
Pertussis (no sub-clinical case)
7-14 days
Meningococcal 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:
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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
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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 Recognition
Rapid 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
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Hand hygiene
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Respiratory hygiene/cough etiquette
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Use of personal protective equipment (PPE)
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Prevention of needle sticks/sharps injuries
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Cleaning and disinfection of the environment
and equipment
Hand Hygiene
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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
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Respiratory Hygiene/Cough Etiquette
Droplet Precautions
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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
Administrative controls
•Isolation/separation
•Masks
•Effective treatment
Environmental
Controls
Dilution (ventilation)
Removal (Fans)
Decontamination (UVGI)
Respiratory Protectio
AIRBORNE PRECAUTIONS
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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 PRECAUTIONS
Disease
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
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Types of PPE Used in Healthcare Settings
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Gloves – protect hands
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Gowns/aprons – protect skin and/or clothing
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Masks and respirators– protect mouth/nose
– Respirators – protect respiratory tract from airborne
infectious agents
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Goggles – protect eyes
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Face shields – protect face, mouth, nose, and eyes
PPE for Standard Precautions: Based on Risk Assessment
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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:
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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.
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4. Nelson KE, Williams C. Infectious Disease Epidemiology: Theory and practice;(1): 483-496.
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Christie AB. Infectious diseases vol.1 & 2 ;(4): 898-1022.
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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.