Upper respiratory tract infections
From Medical-Wiki
Upper respiratory tract infection (URI) is the most common acute illness seen in an outpatient setting. This general term includes a wide range of conditions including, rhinitis—inflammation of the nasal mucosa; rhinosinusitis or sinusitis—inflammation of the nares and paranasal sinuses; nasopharyngitis (rhinopharyngitis or the common cold)—inflammation of the nares, pharynx, hypopharynx, and uvula; tonsillitis—inflammation of the tonsils, adenoids and lingular tonsils; pharyngitis—inflammation of the pharynx, hypopharynx, uvula, and tonsils; epiglottitis (supraglottitis)—inflammation of the superior portion of the larynx and supraglottic area; laryngitis—inflammation of the larynx; laryngotracheitis—inflammation of the larynx, trachea, and subglotic area; and tracheitis—inflammation of the trachea and subglotic area. Lower respiratory infections contain the entities of epiglottitis, laryngitis, laryngo tracheitis bronchitis, bronchiolitis, and pneumonia. [1]
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Disease process
These illnesses are usually the result of a viral agent, but they may be accompanied by bacterial overgrowths or more rarely be caused primarily by a bacterial agent. The viruses directly invade the mucosa of lining the upper airway.
Person-to-person spread of viruses accounts for most URIs. Inoculation by bacteria or viruses begins when secretions are transferred by hands to respiratory mucosa. The hands have been exposed to pathogens spread from other people already infected through the means of respiratory droplets within the form of coughs or sneezes.
The barriers protecting the respiratory tree are physical, mechanical and immunologic. Nose hair filters and traps particles. Mucus forms a physical barrier. The posterior nasopharynx is angled such that it too traps pathogens. Ciliated cells lower down the respiratory tree trap and transport pathogens to the pharynx where they may then be swallowed into the stomach.
Further down the respiratory tree, adenoids and tonsils are part of the immune mechanism that utilize both immunoglobulin A and cellular immunity.
Incubation times vary from 1 to 7 days for the more common pathogens to as long as 4 to 6 weeks for Epstein-Barr virus.
Local swelling, fever, edema, secretions, and erythema are a combination of toxins released from the pathogens as well as the body’s immune response. As the infection extends to adjacent structures, sinusitis, otitis media, epiglotittis, laryngitis, tracheobronchitis, and pneumonia may develop.
Morbidity & mortality
Inflammation of the epiglottis and larynx are the most acute risk because they involve the narrowest portions of the airway. This narrowing has the potential to cause acute respiratory distress and even death in children—the population most at risk because of the smaller absolute diameter of their airways. However, adults, with or without congenital narrowing, may experience acute problems as well.
Epidemiology
During the colder months, more time is spent indoors. This means there is closer contact between all groups of people, increasing the opportunity for spread of disease. Further, the drop in humidity associated with cold weather creates an environment conducive to the survival of respiratory agents. Low humidity increases the friability of respiratory tissues. Because of these factors, there is a seasonality of respiratory infections.
In the U.S., URIs begin an increase in frequency in late August or early September that continues through March or April. Epidemics or miniepidemics peak in incidence in late winter or early spring.
Various pathogens have varying peak incidences. Rhinoviruses are peak in the spring, summer, and early autumn. Coronaviruses peak in the winter and early spring. Enteroviruses occur most commonly in summer and early fall. Adenoviruses peak the late winter, spring, and early summer, but can be seen year around. Influenza is active from November until March. Parainfluenza viruses (PIV) have a biennial pattern, with the leading cause of croup in children, with human PIV type 1, typically peaking in the autumn during odd-numbered years. Human PIV type 2 may show a biennial fall pattern, and PIV type 3 peaks in the spring and early summer. Human metapneumovirus (hMPV) ioccurs year around but peaks between December and February. [2]
Group A streptococcal bacteria is estimated to cause between 5% and 25% of all cases of pharyngitis. It is rare below the age of 2. Influenza virus infects somewhere between 5% and 20%. By the time they are 40, roughly 95% of Americans have antibodies against EBV. Childhood EBV appears as a common run of the mill URI. In adolescents, 35% to 50% of EBV infections take the form of mononucleosis.
Treatment
One of the most discussed aspects of URIs is the use of antibiotics. Since viruses are the primary pathogens involved in these infections, the use of antibiotics would seem to play no role in their treatment. However, the incidence of secondary otitis media and sinusitis and the possibility of URIs extending into the lower respiratory tract muddy this philosophy. In addition, patient pressure on physicians to “do something” adds to the debate. However, it is readily apparent that the widespread use of antibiotics when they are not needed has profoundly increased bacterial resistance.
Two recent Cochrane Reviews have cast some light on this topic. One concluded “A runny nose with colored discharge (acute purulent rhinitis) is associated with the common cold. Results suggest that antibiotics may improve this aspect but antibiotics are not recommended as an initial treatment for this condition as most people get better without them.” [3]
The second concluded,” One way for doctors to reduce their use is to prescribe them 'delayed', (meaning providing the prescription, but advising that the patient delay their use in the hope symptoms resolve first). Delay is effective at reducing antibiotic use.” [4]
Taken together, these suggest a compromise for the PCP faced with the dilemma of URIs and antibiotics with regard to mucopurulent rhinorrhea—delay antibiotic use, but it does appear to shorten the presence of purulent rhinorrhea. The reviews do not estimate the risk versus benefit factors for preventing persistence of purulent rhinorrhea versus antibiotic intervention.
With regard to antibiotics for pharyngitis, another Cochrane Review concluded, “This review of trials found that antibiotics shorten the illness by an average of about one day. They can reduce the chance of rheumatic fever in communities where this complication is common.” [5]
This study regarded in the context of the classic Casper Study that demonstrated that an aggressive culture program for the identification of Group A beta hemolytic strep reduces the incidence of rheumatic fever ten-fold suggest that a culture regimen is appropriate for deciding when antibiotics should be used to prevent rheumatic fever, but their use on a routine basis is not.
A Cochrane Review that considered the use of antibiotics for otitis media concluded, “This review found that long-term antibiotics (over at least six weeks) almost halved the risk of further infections. There was not enough information to know if antibiotics reduced acute otitis media with perforation or chronic suppurative otitis media, or improved long-term outcomes. Antibiotics did not appear to be a frequent cause of significant side effects (for example, allergic reactions or diarrhoea).” [6]
This conclusion is supported when one considers the reduced incidence of deafness and mastoiditis present in the general population.
