Transmission of organisms causing URIs occurs by aerosol, droplet, or direct hand-to-hand contact with infected secretions, with subsequent passage to the nares or eyes.8 Thus, transmission occurs more commonly in crowded conditions. Direct invasion of the respiratory epithelium results in symptoms corresponding to the area(s) involved.
Sinusitis and acute bronchitis are frequently preceded by a common cold. Sinonasal allergies, anatomic abnormalities such as a deviated nasal septum, sinus ostial blockade caused by mucosal edema, immunodeficiency disorders such as hypogammaglobulinemia and human immunodeficiency virus infection, and abuse of nasally inhaled cocaine predispose to the development of acute sinusitis.3
Most influenza epidemics in the 20th century were caused by the influenza A virus, but a few were caused by the influenza B virus. Most epidemics are believed to spread from schoolchildren to their families. Annual influenza epidemics result from the transmission of a mutated influenza virus for which most humans do not have immunity (antigenic drift). Pandemics, on the other hand, occur when a totally new influenza virus is transmitted to humans from other species, most commonly swine and birds (antigenic shift). People older than 65 years and those with comorbidities are at higher risk than healthy people for hospitalization and death because of exacerbation of their underlying medical conditions as a result of influenza.
Transmission of organisms causing URIs occurs by aerosol, droplet, or direct hand-to-hand contact with infected secretions, with subsequent passage to the nares or eyes.8 Thus, transmission occurs more commonly in crowded conditions. Direct invasion of the respiratory epithelium results in symptoms corresponding to the area(s) involved.Sinusitis and acute bronchitis are frequently preceded by a common cold. Sinonasal allergies, anatomic abnormalities such as a deviated nasal septum, sinus ostial blockade caused by mucosal edema, immunodeficiency disorders such as hypogammaglobulinemia and human immunodeficiency virus infection, and abuse of nasally inhaled cocaine predispose to the development of acute sinusitis.3Most influenza epidemics in the 20th century were caused by the influenza A virus, but a few were caused by the influenza B virus. Most epidemics are believed to spread from schoolchildren to their families. Annual influenza epidemics result from the transmission of a mutated influenza virus for which most humans do not have immunity (antigenic drift). Pandemics, on the other hand, occur when a totally new influenza virus is transmitted to humans from other species, most commonly swine and birds (antigenic shift). People older than 65 years and those with comorbidities are at higher risk than healthy people for hospitalization and death because of exacerbation of their underlying medical conditions as a result of influenza.
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