Review of Medical Microbiology and Immunology, 13th Edition

75. Upper Respiratory Tract Infections

Contributed by Peter Chin-Hong, MD

CHAPTER CONTENTS

Introduction

Otitis Media

Sinusitis

Pharyngitis

Common Cold

Croup

Laryngitis

Epiglottitis

INTRODUCTION

Infections of the upper respiratory tract are a common ambulatory care complaint, resulting in a large proportion of office visits. Although the vast majority of infections are viral and are self-limited, some may require hospitalization, particularly in the pediatric population. Bacterial etiologies of some of the common upper respiratory tract infections may be primary or superinfections of the original viral processes and are amenable to treatment (Table 75–1).

TABLE 75–1 Common Infections of the Upper Respiratory Tract

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OTITIS MEDIA

Definition

Otitis media is an infection of the middle ear caused by either viruses or bacteria. Otitis media can be either acute or chronic. The information in this chapter refers to acute otitis media.

Pathophysiology

Any process that leads to eustachian tube obstruction can result in fluid retention and concomitant infection of the middle ear. The most common predisposing factors are upper respiratory tract infections and seasonal allergic rhinitis. Otitis media is very common in children under the age of 3 years because they have a small opening of the eustachian tube that is easily blocked by the inflammation caused by a viral infection or an allergic response.

Clinical Manifestations

Patients present with ear pain and pressure, often accompanied by an upper respiratory tract infection. In infants, the ear pain may manifest as ear pulling. Patients may also complain of decreased hearing and fever. On examination, the tympanic membrane is erythematous (Figure 75–1A and B) with a loss of the light reflex and decreased mobility. In some cases, the tympanic membrane may bulge and then rupture.

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FIGURE 75–1 A: Normal tympanic membrane in 6-year-old child. B: Otitis media in 3-year-old child. Note bulging tympanic membrane and loss of light reflex. (From Tintinalli JE et al: Tintinalli’s Emergency Medicine: A Comprehensive Study Guide. 7th ed. New York: McGraw-Hill, 2009. Copyright © 2009 by The McGraw-Hill Companies, Inc. Courtesy of Dr. Shelagh Cofer, Department of Otolaryngology, Mayo Clinic.)

Pathogens

Both bacteria and viruses cause otitis media. Among bacteria, Streptococcus pneumoniae is the most common cause. Nontypeable strains of Haemophilus influenzae and Moraxella catarrhalis are also common causes. Among viruses, respiratory syncytial virus, coronaviruses, and rhinoviruses are commonly involved.

Diagnosis

Otitis media is usually diagnosed clinically. If the membrane ruptures, a sample of the exudate can be analyzed by Gram stain and culture. If indicated, tympanocentesis can be done to relieve pressure before the drum ruptures and to obtain a specimen for culture.

Treatment

Amoxicillin orally is usually the drug of choice together with nasal decongestants to open the eustachian tube. In cases of bacterial resistance, amoxicillin-clavulanate (Augmentin) may be used.

Prevention

Recurrent episodes of otitis media can be suppressed by prophylactic antibiotics such as amoxicillin or sulfisoxazole. Ventilating tubes may be inserted as a strategy to prevent recurrent infections. The conjugate pneumococcal vaccine is effective in preventing invasive pneumococcal disease but is less effective in preventing otitis media.

SINUSITIS

Definition

Sinusitis is inflammation of the paranasal sinuses. It can be either acute or chronic. Acute infections are considered those with symptoms lasting less than 4 weeks. The information in this chapter refers to acute sinusitis.

Pathophysiology

Impaired mucociliary clearance caused by viral infection or allergic rhinitis can obstruct the orifice of the sinus. Mucus then accumulates in the sinus cavity. Stasis can lead to bacterial overgrowth and superinfection. Sinusitis frequently involves the maxillary sinus because the ostium of that sinus is located superior to most of the sinus and drainage of mucus has to occur against gravity. Drainage of the other sinuses is aided by gravity.

Clinical Manifestations

Clinical manifestations include purulent nasal discharge, nasal congestion, facial or sinus pain, decreased sense of smell, and fever. Headache and malodorous breath may be present.

Pathogens

Many cases begin with a viral upper respiratory tract infection. Bacterial superinfection can then occur. In the case of acute bacterial sinusitis, common organisms are S. pneumoniae, H. influenzae, and M. catarrhalis, as in the case of acute otitis media. Staphylococcus aureus also causes sinusitis but less commonly. In immunocompromised patients and diabetics, sinusitis caused by fungi such as Aspergillus or Mucor may occur.

Diagnosis

Sinusitis is often diagnosed based on a typical constellation of symptoms and clinical findings. Computed tomography scan of the sinuses is a very sensitive modality for indicating inflammatory processes of the sinus. However, in the absence of bony destruction, these are nonspecific findings for diagnosing clinically significant sinusitis requiring antibiotic therapy (Figure 75–2).

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FIGURE 75–2 Sinusitis. Arrow points to opacified maxillary sinus seen in CT scan of head. (Reproduced with permission from Brunicardi FC, Andersen D, Billiar T, et al: Schwartz’s Principles of Surgery, 8th ed. New York, McGraw-Hill, 2004.)

Treatment

If symptoms are severe, antibiotics are given in concert with intranasal corticosteroids, as well as nasal decongestants. Amoxicillin is the drug of choice, but if resistance is a concern, then amoxicillin-clavulanate (Augmentin) is used. In mild cases, antibiotics are not normally used unless the symptoms have lasted for longer than 10 to 14 days.

Prevention

There is no convincing evidence that the pneumococcal vaccine and the H. influenzae type B vaccine have a significant effect in reducing sinusitis caused by these organisms.

PHARYNGITIS

Definition

Pharyngitis is inflammation of the throat caused primarily by viruses. Approximately 10% of cases of pharyngitis are caused by Streptococcus pyogenes (group A Streptococcus [GAS]). Streptococcal pharyngitis (strep throat) is important because poststreptococcal immune sequellae, such as rheumatic fever, may occur.

Clinical Manifestations

Patients will complain of sore throat that is worse when swallowing. Fever may also be present. Typical symptoms associated with an upper respiratory tract infection (rhinorrhea, sinus tenderness, ear pain, cough) may accompany the sore throat. On examination, an inflamed pharynx, tonsils, and palate are typically seen. A grayish exudate is often present on the tonsils. Tender, anterior cervical lymphadenopathy may be present. Petechiae on the palate may also be a diagnostic clue for GAS (Figure 75–3).

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FIGURE 75–3 Pharyngitis caused by Streptococcus pyogenes. Note inflamed pharynx, tonsils, and palatal petechiae. (The white circles and curved lines are an artifact of the lighting during photography.) (Courtesy of Dr. Heinz F. Eichenwald, Public Health Image Library, Centers for Disease Control and Prevention.)

Pathogens

Bacteria

S. pyogenes (GAS) is the most important bacterial cause. Group C and G streptococci also cause pharyngitis but are not antecedents to rheumatic fever. Pharyngitis caused by Neisseria gonorrhoeae is likely to be the result of sexual activity and, if it occurs in children, is considered as a sign of child abuse. Mycoplasma pneumoniae, Chlamydia pneumoniae, and Arcanobacterium haemolyticum also cause pharyngitis. In certain countries where the diphtheria vaccine is not widely used, Corynebacterium diphtheriae is a significant cause of pharyngitis, often accompanied by a pseudomembrane. Fusobacterium necrophorum, a gram-negative anaerobe, can cause pharyngitis accompanied by septic thrombophlebitis (Lemierre’s syndrome). Note that although S. pneumoniae and H. influenzae colonize the oropharynx, they do not cause pharyngitis.

Viruses

Most cases of pharyngitis are caused by respiratory viruses, such as adenovirus, influenza A and B viruses, parainfluenza virus, rhinovirus, and coronavirus. Other viral causes include Coxsackie virus (herpangina), Epstein–Barr virus (infectious mononucleosis), and herpes simplex virus, especially type 1. Human immunodeficiency virus causes an acute retroviral syndrome that includes pharyngitis as one of its components.

Diagnosis

The main strategy in diagnostics is to establish whether there is infection with GAS. This is because GAS is treatable, and timely intervention may prevent complications such as acute rheumatic fever. The Centor criteria are criteria that may be used to aid in the diagnosis of GAS. These criteria include tonsillar exudates, tender anterior cervical adenopathy, fever, and absence of cough. Rapid antigen detection tests for GAS and throat culture are often used to confirm the diagnosis.

It can be difficult to distinguish between a bacterial pharyngitis and a viral pharyngitis when examining the throat. Figure 75–4 shows extensive exudates on the tonsils in pharyngitis caused by Epstein–Barr virus. A throat culture is the most reliable method of determining whether S. pyogenes is the cause.

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FIGURE 75–4 Pharyngitis caused by Epstein–Barr virus. Note several whitish exudates on tonsils (red arrow). (Reproduced with permission from Kane KSM, Lio P, Stratigos A, Johnson R: Color Atlas & Synopsis of Pediatric Dermatology, 2nd ed. New York, McGraw-Hill, 2010.)

Treatment

If GAS is diagnosed, treatment with penicillin G, penicillin V, or amoxicillin is undertaken. In penicillin-allergic patients, erythromycin or cephalexin can be used. The overuse of antibiotics, such as penicillin and macrolides, in cases of pharyngitis continues to be a problem. Although only 10% of sore throats are bacterial, data show that 60% of sore throats are treated with antibiotics, resulting in unnecessary expense, adverse effects, and the selection of resistant bacteria.

Prevention

There is a vaccine against C. diphtheriae and influenza virus but not against pharyngitis caused by S. pyogenes or any other bacterial or viral cause. Long-term carriers of GAS should not be treated because there is no evidence that such treatment prevents spread of the organism to close contacts or the development of complications such as acute rheumatic fever. Note that children who have rheumatic heart disease should receive penicillin orally for many years to prevent infection by S. pyogenes, which could cause a flare of their rheumatic heart disease.

COMMON COLD

Definition

The common cold is a viral infection of the upper respiratory tract, including some or all of the following structures: the nose, throat, sinuses, eustachian tubes, trachea, and larynx.

Pathophysiology

The viruses that cause the common cold are transmitted primarily by aerosols generated by sneezing, or by direct contact. Direct contact involves either hand-to-hand contact or hand-to-surface contact. The nonenveloped viruses such as rhinoviruses and adenoviruses are particularly stable in the environment and are often transmitted by hand-to-surface contact.

The common cold and other respiratory infections such as influenza occur more often in the winter months than in the summer months in both the Northern and Southern hemispheres. The reason for this seasonality is uncertain.

Clinical Manifestations

Clinical manifestations include nasal congestion, decreased sense of smell, rhinorrhea (watery nasal discharge without purulence), and sneezing. Patients also complain of general malaise and sore throat. In some cases, headache may also be reported.

Pathogens

Rhinoviruses (more than 100 serotypes) are the most common etiology (up to 50%). Coronaviruses, adenoviruses, and enteroviruses such as Coxsackie viruses are other causes. Viruses such as parainfluenza virus and respiratory syncytial virus are also possible causes of the common cold, although they primarily cause other diseases (croup and bronchiolitis, respectively).

Diagnosis

The common cold is usually diagnosed clinically. Erythematous and edematous nasal mucosa is seen on physical examination. Conjunctival and pharyngeal injection may also be seen. (Injection in this context means hyperemia of small blood vessels.)

Treatment

Generally, symptomatic therapy is offered. It is controversial whether zinc salts may be helpful. Zinc acetate in doses greater than 75 mg/d may reduce the duration of symptoms. Other strategies include oral decongestants and buffered hypertonic saline nasal irrigation. If used for more than a few days, nasal sprays may be associated with rebound congestion after stopping.

Prevention

Although many vitamins and herbal therapies (e.g., echinacea) have been evaluated, there has been no conclusive evidence that any one therapy is helpful. Vitamin C taken prophylactically may be helpful in a population of cold weather athletes. However, when vitamin C was tested in the general population (rather than athletes), its ability to prevent colds was marginal. Handwashing may prevent the transmission of respiratory viruses. There is no vaccine against any virus that causes the common cold.

CROUP

Definition

Croup is an inflammation of the larynx, trachea, and large bronchi (laryngotracheobronchitis).

Clinical Manifestations

Inspiratory stridor is the key finding, together with a barking cough and a hoarse voice. Symptoms may begin in a subtle fashion with nasal irritation and congestion and then rapidly progress to stridor over a day.

Pathogens

Parainfluenza viruses, especially type 1, are the most common cause. Respiratory syncytial virus and influenza virus account for 1% to 10% of cases.

Diagnosis

The diagnosis is usually made clinically. Plain radiographs may show a “steeple sign” (subglottic tracheal narrowing results in an inverted “V” shape) (Figure 75–5).

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FIGURE 75–5 Croup. This X-ray shows the “steeple sign” of croup in a 12-year-old child. The red arrow points to the upper tip of the steeple. The steeple represents the constriction caused by an inflamed larynx and trachea. (Reproduced with permission from Stone CK, Humphries RL (eds). Current Diagnosis and Treatment of Emergency Medicine. 7th ed. New York: McGraw-Hill. Copyright © 2011 by The McGraw-Hill Companies, Inc.)

Treatment

Patients with moderate to severe symptoms may be given corticosteroids such as dexamethasone, with or without epinephrine. There is no antiviral drug therapy.

Prevention

There is no vaccine against parainfluenza virus.

LARYNGITIS

Definition

Laryngitis is inflammation of the vocal folds of the larynx.

Clinical Manifestations

Clinical manifestations include hoarseness and the inability to speak (aphonia). Laryngitis may be accompanied or preceded by an upper respiratory infection.

Pathogens

Parainfluenza viruses and rhinoviruses are the most common causes of laryngitis. Other respiratory viruses such as influenza virus, adenovirus, and coronavirus have been isolated from patients. Bacteria such as S. pyogenes, M. catarrhalis, and H. influenzae have also been isolated.

Diagnosis

The diagnosis of laryngitis is primarily made clinically.

Treatment

Treatment includes hydration and voice rest. Antibiotics are not needed.

Prevention

There is no vaccine against parainfluenza virus and rhinoviruses. There is no convincing evidence that the influenza virus vaccine and the H. influenzae type B vaccine have reduced the number of cases of laryngitis.

EPIGLOTTITIS

Definition

Epiglottitis is an inflammation of the epiglottis.

Clinical Manifestations

Patients present with rapidly worsening sore throat and odynophagia (pain on swallowing) or dysphagia (difficulty in swallowing). Pain may be out of proportion to physical examination findings. Airway obstruction can occur in severe cases. Epiglottitis in young children should be treated as a medical emergency.

Pathogens

H. influenzae type B is, by far, the most common cause, although the widespread use of the vaccine against H. influenzae type B has greatly reduced the incidence of epiglottitis. Less common pathogens include other H. influenzae types, S. pneumoniae, S. pyogenes, and S. aureus.

Diagnosis

Diagnosis is made by visualization of the epiglottis. If indirect laryngoscopy (done primarily in children) is performed, a swollen and erythematous “cherry-red” epiglottis may be visualized. On lateral plain X-rays, an enlarged epiglottis may be seen as a “thumb” sign (Figure 75–6).

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FIGURE 75–6 Epiglottitis. Note enlarged epiglottis (white arrow) in a lateral view of X-ray of neck. (Reproduced with permission from Longo DL et al (eds). Harrison’s Principles of Internal Medicine. 18th ed. New York: McGraw-Hill, 2012. Copyright © 2012 by The McGraw-Hill Companies, Inc.)

Treatment

Treatment involves intravenous ceftriaxone. Some centers add corticosteroids to reduce inflammation, but its effects are undocumented. An adequate airway must be maintained.

Prevention

Prevention includes immunization against H. influenzae type B and S. pneumoniae. Rifampin prophylaxis should be given to close household contacts to reduce oropharyngeal carriage.