Environmental Engineering Reference
In-Depth Information
Acute respiratory infections (ARIs) are the most common of human illnesses, which we take for
granted because they occur so often and are usually mild. However, among children under 5 years
of age, approximately 17% of all deaths (1.7 million in 2004) are due to ARIs, primarily pneumonia,
which is the largest single cause of death in this age group. 21 Respiratory tract infections in child-
hood may have long-term sequelae, including loss of lung function after severe episodes of lower
respiratory tract infection, the development of asthma or bronchiectasis (Section 12.2.2), and an
increased risk of developing COPD in adulthood. 23
Three-quarters of ARI deaths in children under 5 years of age are in Africa and Southeast Asia.
Respiratory syncytial viral (RSV) is believed to be the most important viral cause of ARI, respon-
sible for an estimated 66,000−199,000 deaths in children under 5 years of age (99% in developing
countries). 24 The higher childhood mortality in developing countries probably relects poorer nutri-
tion and immunization practices and more frequent low birth weight, crowding, and exposure to
indoor and outdoor air pollutants. 25 Disadvantaged population groups bear the greatest burden, but
communicable diseases occurring anywhere are of concern to everyone, given the connectedness
of all parts of the world via voluntary and involuntary human migrations and rapid international air
travel. 26
Outbreaks of previously unrecognized airborne infectious diseases seriously affect the global
economy, for example, Legionnaires' disease in the 1970s, severe acute respiratory syndrome
(SARS) in 2002-2003, and the 2009 pandemic inluenza A (H1N1) more recently. Communicable
disease outbreaks are designated epidemics when the occurrence in a community or region clearly
exceeds normal expectancy, and epidemics are designated pandemics when they occur worldwide
or over a wide geographic area. 27 The origins of emerging infectious diseases also are signiicantly
correlated with socio-economic, environmental, and ecological factors. Unfortunately, the majority
of scientiic and surveillance efforts focus on countries from which new diseases are least likely to
originate. 28
The economic cost of lost productivity from the common cold has been estimated at over $25
billion in the United States, and mean productivity losses in Sweden from allergic rhinitis and the
common cold have been estimated at 5.1 days €653/worker/year. 29,30 Of the common ARIs, inlu-
enza produces the most severe illness and accounts for the greatest number of days of restricted
activity in the United States. 31,32 The total economic burden in the United States of annual inluenza
epidemics has been estimated at $87 billion. 33
Inluenza strains with high transmissibility and pathogenicity, such as H5N1 and H1N1, continue
to evolve and may be responsible for the next global pandemic. 34 As of August 6, 2010, a total of
214 countries and overseas territories or communities reported laboratory conirmed cases of pan-
demic inluenza H1N1 2009, including over 18,449 deaths. 35 This pandemic virus disproportion-
ately affected children, who in turn posed a risk for secondary household transmission, especially
to caregivers and siblings. 36,37 The household transmissibility of this inluenza virus was lower than
past pandemic strains, with most transmission occurring shortly before or after symptom onset. The
eficacy of hand hygiene, respiratory protection, cough etiquette, isolation, social distancing, and
travel restrictions to prevent transmission has been dificult to evaluate. 37,38 There is some evidence
that the wearing of face masks or respirators during illness can protect contacts and help reduce
transmission of respiratory tract infections; however, there is insuficient evidence that the use of
respiratory protection protects wearers from infection. 39,40
12.2.1.1  Transmission of Infectious Agents
Inhalation is the most important and eficient route by which infectious agents enter the human
body, and infections contracted by this route are the most dificult to control. 41 The great pandemics
in human history (e.g., plague and inluenza) as well as many common childhood infections (e.g.,
measles, rubella, varicella, and mumps) are acquired from the respiratory secretions of others (Table
12.1). Transmission by air allows an infectious agent to reach a larger number of potential hosts than
would be possible if infected individuals had to come into direct contact to transfer microorganisms
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