In the Northern hemisphere, viral epidemics cause up to 80% of all
respiratory illnesses. The most common infections are caused by six viral
groups: rhinovirus (RVs), respiratory syncytial virus, influenza virus,
parainfluenza virus, corona virus, and adenovirus. In one study of 285 children
admitted to hospital with lung infection, viruses were identified in 125 -
respiratory syncytial virus (107), influenza (9) and parainfluenza type 3 (9).
Clinical and radiologic diagnoses included bronchiolitis (127), interstitial
pneumonia (47) and lobar pneumonia (91).
Colds are viral infections limited to the ear, nose and throat. Patients
spread viruses by coughing and sneezing, spraying airborne droplets and by
leaving viruses on every object they touch with contaminated hands. Adults
contaminate their hands in 39% of cases, and virus has been found on 6% of
objects in their homes. Viruses remain intact for hours to several days on
surfaces. In hospitals, face masks provide some protection, but wearing gloves
and washing hands may be as important. Influenza viruses are transmitted by
direct and indirect contact, as well as by airborne droplet contact. Airborne
infection by droplets can be reduced by wearing cellulose face masks that
conform to NIOSH N100 standards. Proper ventilation with filtration and
ultraviolet air disinfection units also reduce illness rates in buildings.
Rhinoviruses often referred to as “cold viruses” cause the majority of
respiratory illnesses. Other viruses contribute to waves of colds, coughs,
bronchitis, asthma and pneumonia that pass through every human population in
epidemic patterns. Colds are rhinovirus infections that are usually mild and
self-limiting but are more serious in premature babies and children with chronic
diseases or immunosuppression. The average child can expect to have four to
eight rhinovirus infections per year, and adults have three to five infections.
Respiratory Syncytial Virus is spread by coughing and sneezing; by
close contact with sick patients or by hand contamination. Infection develops in
care -givers who touch their eyes or nose with contaminated fingers.
Adenoviruses While Influenza viruses are well-known and epidemics of
more virulent influenza strains are feared, other less known viruses, especially
adenoviruses, tend to be common and can produce severe illnesses.
For example, adenoviruses are the second most prevalent cause of acute lower
respiratory infection of viral origin in children under four years of age in
Buenos Aires, Argentina. Pneumonia was observed in 71% and bronchiolitis in 29%
of children admitted to hospital with adenovirus infection. Wheezing occurred in
58% of the children. Four children died (a fatality rate of 16.7%).
Adenoviruses have emerged as important pathogens in immunocompromised
patients, in whom disseminated disease occurs frequently and is associated with
a high mortality rate. For over 25 years, the US military controlled
adenoviral respiratory infections through immunization of its members. A group
of Navy physicians reported a “large epidemic of respiratory illness due to
adenovirus in healthy young adults” after adenovirus vaccine supplies were
The US military medical services are perhaps best equipped to diagnose and
treat adenovirus infection which cause outbreaks of disease among military
recruits. A National Surveillance for Emerging Adenovirus Infections system
includes military and civilian laboratories at 15 sites in the USA. Fifty-one
adenovirus serotypes have been identified. In 2007 the emergence of a virulent
Ad14 variant spread through the United States with some deaths. Ad14 infection
was described initially in 1955 and was responsible for an epidemic acute
respiratory disease in military recruits in Europe in 1969. In 2001-2002, Ad14
was associated with approximately 8% of respiratory adenoviral infections in the
pediatric ward of a Taiwan hospital, with approximately 40% of Ad14 cases in
children aged 4-8 years manifesting as lower airway disease. During the years,
2004-2007, the US surveillance system detected 17 isolates of Ad14 from seven
sites. During March-June 2007, a total of 140 additional cases of confirmed Ad14
respiratory illness were identified in Oregon, Washington, and Texas.
Fifty-three (38%) of these patients were hospitalized, including 24 (17%) who
were admitted to intensive care units (ICUs); nine (5%) patients died
Metapneumovirus Ulloa-Gutierrez reported that metapneumovirus was
identified as a cause of acute upper and lower respiratory tract infection in
children and adults worldwide, with most episodes occurring during the winter
months. Most children have been infected by five years of age. The illness in
young children may be life-threatening bronchiolitis or pneumonia. Patterns of
adult infection are not well-understood.
Influenza viruses cause epidemic respiratory illness every winter in
most countries on the planet. Influenza often begins with cold symptoms and
progresses to involve the lungs. Most patients develop a chronic cough that can
last for weeks. Pneumonia can develop and is a common cause of death among more
Much publicity has been given to the possibility of an especially virulent
strain emerging that will increase the death toll from thousands per year in the
US and Canada to millions. Some virologists were concerned that influenza virus
epidemics in birds would produce a newly virulent human virus. The World Health
Organization warned that the world is not prepared for the next pandemic. As of
January 2006, the strain of avian influenza, A (H5N1), has been identified in
only 148 human, 79 of them fatal, from direct contact with infected birds. The
strain was first detected in Hong Kong in 1997 and has spread through Southeast
Asia and then in Russia and Turkey. In 2009 a H1N1 variant ("swine flu") emerged
and caused another media frenzy; the WHO declared a "pandemic" and despite
reports of a relatively mild illness with a low mortality rate, news
anchors began to refer to a "deadly virus". The positive aspect of the scare
tactics was increased international cooperation in monitoring the spread
of the virus and increased funding of vaccine development. Some of the fear was
generated by comparison with the 1917 flu pandemic caused by another H1A1 virus.
The truth is that speculations based on very limited knowledge of that pandemic
are likely to be wrong. While you can argue that every year, influenza and many
other types of viruses create pandemics and every year more virulent strains
could emerge, there is no real knowledge that allows experts to predict what
will happen next.
Annual influenza shots are recommended for all persons at risk, but the
vaccines are based on last year’s virus strains with no guarantee that they will
protect against newly emergent viruses. Influenza viruses constantly mutate.
During the winter flu season, people who develop respiratory illness have a
responsibility to reduce their ability to spread the disease. An altruistic act
is to quarantine oneself until the acute illness subsides.
Viruses are spread by contaminated hands and airborne droplets projected into
the air by coughing and sneezing. Simple measures to reduce the spread of
viruses are washing hands, covering nose and mouth when sneezing and
coughing, staying home from school and work during respiratory illness. There
are four drugs that inhibit the replication of influenza viruses: amantadine, rimantadine, oseltamivir (Tamiflu) and zanamivir (Relenza). During the
2006 flu season, the US Centers for Disease Control and Prevention reported that
91 percent of the human influenza A (H3N2) virus samples isolated were resistant
to both amantadine and rimantadine. The 2009 H1A1 viruses were sensitive to oseltamivir and zanamivir.