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 depleted.
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 susceptible people.
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 fours 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 appear to be sensitive to oseltamivir and zanamivir.