Upper Respiratory Tract Infections and Other Infections of the Oral Cavity and Neck



Upper Respiratory Tract Infections and Other Infections of the Oral Cavity and Neck



Objectives



1. Explain the anatomy and structures of the upper respiratory tract, including the three parts of the pharynx.


2. Identify the principal causative organism of pharyngitis; name other organisms capable of causing pharyngitis.


3. Define the following conditions: laryngitis, epiglottis, and parotitis. List the etiologic organisms associated with these conditions.


4. Explain the pathogenic mechanisms (virulence factors) associated with Streptococcus pyogenes pharyngitis.


5. Define Vincent’s angina and peritonsillar abscesses. What organism do they share as the causative agent of disease?


6. Describe the disease process caused by pharyngeal infection with Corynebacterium diphtheriae; name the hallmark symptom of this infection and list the complications associated with infection.


7. Differentiate between stomatitis and thrush, and explain the testing process for each disease.


8. Outline the steps used in the culture of specimens for the isolation of Streptococcus pyogenes.


9. Explain the signs and symptoms and pathogenic mechanisms associated with disease caused by Bordetella pertussis. What special requirements are needed to detect this organism in culture?


10. List three types of periodontal infections that require culture to identify the causative agent of infection; name the bacteria associated with these infections.


11. Explain the unique characteristics of C and G streptococcus, and explain how they contribute to their pathogenesis.



General Considerations


Anatomy


The respiratory tract is generally divided into two regions, the upper and the lower.


The upper respiratory tract includes all the structures down to the larynx: the sinuses, throat, nasal cavity, epiglottis, and larynx; the throat is also called the pharynx. These anatomic structures are shown in Figure 70-1.


image
Figure 70-1 The pharynx, including its three divisions and nearby structures.

The pharynx is a tubelike structure that extends from the base of the skull to the esophagus (see Figure 70-1). Made of muscle, this structure is divided into three parts:



The oropharynx and nasopharynx are lined with stratified squamous epithelial cells that are teeming with microbial flora. The tonsils are contained within the oropharynx; the larynx is located between the root of the tongue and the upper end of the trachea.



Pathogenesis


An overview of the pathogenesis of respiratory tract infections is presented in Chapter 69. It is important to keep in mind that upper respiratory tract infections may spread and become more serious because the mucosa (mucous membrane) of the upper tract is continuous with the mucosal lining of the sinuses, eustachian tube, middle ear, and lower respiratory tract.



Diseases of the Upper Respiratory Tract, Oral Cavity, and Neck


Upper Respiratory Tract


Diseases of the upper respiratory tract are named according to the anatomic sites involved. Most of these infections are self-limiting, and the majority of infections are of viral origin.



Laryngitis


Acute laryngitis is usually associated with the common cold or influenza syndromes. Characteristically, patients complain of hoarseness and lowering or deepening of the voice. Acute laryngitis is generally a benign illness.


Acute laryngitis is almost exclusively associated with viral infection. Although numerous viruses can cause laryngitis, influenza and parainfluenza viruses, rhinoviruses, adenoviruses, coronavirus, and human metapneumovirus are the most common etiologic agents. If examination of the larynx reveals an exudate or membrane on the pharyngeal or laryngeal mucosa, streptococcal infection, mononucleosis, or diphtheria should be suspected (see the discussion about miscellaneous infections caused by other agents, presented later in this chapter). Chronic laryngitis, although less frequently associated with infectious agents, may be caused by bacteria or fungal isolates. Infections have been identified that are associated with methicillin-resistant Staphylococcus aureus (MRSA) and Candida spp.



Laryngotracheobronchitis


Another clinical syndrome closely related to laryngitis is acute laryngotracheobronchitis, or croup. Croup is a relatively common illness in young children, primarily those younger than 3 years of age. Of significance, croup can represent a potentially more serious disease if the infection extends downward from the larynx to involve the trachea or even the bronchi. Illness is characterized by variable fever, inspiratory stridor (difficulty in moving enough air through the larynx), hoarseness, and a harsh, barking, nonproductive cough. These symptoms last for 3 to 4 days, although the cough may persist for a longer period. In young infants, severe respiratory distress and fever are common symptoms.


Similar to the etiologic agents of laryngitis, viruses are a primary cause of croup; parainfluenza viruses are the major etiologic agents. In addition to parainfluenza viruses, influenza viruses, respiratory syncytial virus, and adenoviruses can also cause croup.


Also capable of causing croup, though not as frequently, are Mycoplasma pneumoniae, rhinoviruses, and enteroviruses.



Epiglottitis


Epiglottitis is an infection of the epiglottis and other soft tissues above the vocal cords. Infection of the epiglottis can lead to significant edema (swelling) and inflammation. Most commonly, children between the ages of 2 and 6 years of age are infected. These children typically present with fever, difficulty in swallowing because of pain, drooling, and respiratory obstruction with inspiratory stridor. Epiglottitis is a potentially life-threatening disease because the patient’s airway can become completely obstructed (blocked) if not treated.


In contrast to laryngitis, epiglottitis is usually associated with bacterial infections. In the past, 2- to 4-year-old children were typically infected with Haemophilus influenzae type b as the primary cause of epiglottitis. However, due to the common use of Haemophilus influenzae type b conjugated vaccine, the typical patient is an adult with a sore throat. Other organisms occasionally implicated are streptococci and staphylococci. Diagnosis is established on clinical grounds, including the visualization of the epiglottis, which appears swollen and bright red in color. Bacteriologic culture of the epiglottis is contraindicated because swabbing of the epiglottis may lead to respiratory obstruction. Of importance, H. influenzae bacteremia usually occurs in children with epiglottitis caused by this organism.



Pharyngitis, Tonsillitis, and Peritonsillar Abscesses



Pharyngitis and Tonsillitis.

Pharyngitis (sore throat) and tonsillitis are common upper respiratory tract infections affecting both children and adults. Acute pharyngitis is an illness that frequently causes people to seek medical care.





Epidemiology/Etiologic Agents.

Most cases of pharyngitis occur during the colder months and often accompany other infections, primarily those caused by viruses. Patients with respiratory tract infections caused by influenza types A and B, parainfluenza, coxsackie A, rhinoviruses, or coronaviruses frequently complain of a sore throat. Pharyngitis, often with ulceration, is also commonly found in patients with infectious mononucleosis caused by either Epstein-Barr virus or cytomegalovirus. Although less common, pharyngitis caused by adenovirus or herpes simplex virus is clinically severe. Finally, acute retroviral syndrome caused by human immunodeficiency virus 1 (HIV-1) is associated with acute pharyngitis.


Although different bacteria can cause pharyngitis or tonsillitis, the primary cause of bacterial pharyngitis is Streptococcus pyogenes (or group A beta-hemolytic streptococci). Viral pharyngitis or other causes of pharyngitis/tonsillitis must be differentiated from that caused by S. pyogenes, because pharyngitis resulting from S. pyogenes is treatable with penicillin and a variety of other anti-microbials, whereas viral infections are not. In addition, treatment is of particular importance because infection with S. pyogenes can lead to complications such as acute rheumatic fever and glomerulonephritis. These complications are referred to as poststreptococcal sequelae (diseases that follow a streptococcal infection) and are primarily immunologically mediated; these sequelae are discussed in greater detail in Chapter 15. S. pyogenes may also cause pyogenic infections (suppurations) of the tonsils, sinuses, and middle ear, or cellulitis as secondary pyogenic sequelae after an episode of pharyngitis. Accordingly, streptococcal pharyngitis is usually treated to prevent both the suppurative and nonsuppurative sequelae, as well as to decrease morbidity.


Although bacteria other than group A streptococci may cause pharyngitis, this occurs less often. Large colony isolates of groups C and G streptococci (classified as Streptococcus dysgalactiae subsp. equisimilis) are pyogenic streptococci with similar virulence traits as S. pyogenes; symptoms of pharyngitis caused by these agents are also similar to S. pyogenes. In contrast to S. pyogenes, these agents are rarely associated with poststreptococcal sequelae, namely glomerulonephritis and possibly rheumatic fever. Recent studies have demonstrated that these streptococci can exchange genetic information with S. pyogenes and thus potentially obtain virulence factors usually associated with S. pyogenes such as M proteins, streptolysin O, and superantigen genes. Arcanobacterium haemolyticum is also a cause of pharyngitis among adolescents. Examples of agents that can cause pharyngitis or tonsillitis are listed in Table 70-1.



Although H. influenzae, S. aureus, and S. pneumoniae are frequently isolated from nasopharyngeal and throat cultures, they have not been shown to cause pharyngitis. Carriage of any of these organisms, as well as Neisseria meningitidis, may have clinical importance for some patients. Cultures of specimens obtained from the anterior nares often yield S. aureus. The carriage rate for this organism is especially high among health care workers, and 10%-30% of the general population can be colonized with this microbe, depending on the population characteristics.


Vincent’s angina, also called acute necrotizing ulcerative gingivitis, or trench mouth, is a mixed bacterial-spirochetal infection of the gingival edge. The infection is relatively rare today, but it is considered a serious disease because it is often complicated by septic jugular thrombophlebitis, bacteremia, and widespread metastatic infection. Adults are more often affected than children; poor oral hygiene is a predisposing factor. Multiple anaerobes, especially Fusobacterium necrophorum, are implicated in this syndrome. Although Gram stain of a throat specimen is usually not predictive, in those patients with symptoms suggestive of Vincent’s angina, Gram stain reveals numerous fusiform, gram-negative bacilli, and spirochetes.




Rhinitis


Rhinitis (common cold) is an inflammation of the nasal mucous membrane or lining. Depending on the host response and the etiologic agent, rhinitis is characterized by variable fever, increased mucous secretions, inflammatory edema of the nasal mucosa, sneezing, and watery eyes. With rare exceptions, rhinitis is typically associated with viral infections (20%-25%); some of these agents are listed in Box 70-1. Rhinitis is common because of the large number of different causative viruses, and reinfections may occur. Bacterial agents associated with rhinitis (10%-15%) include Chlamydia pneumoniae, Mycoplasma pneumoniae, and Group A streptococci.



Box 70-1   Viral Agents That Can Cause Rhinitis





Miscellaneous Infections Caused by Other Agents.



Corynebacterium diphtheriae.

Pharyngitis caused by Corynebacterium diphtheriae is less common than streptococcal pharyngitis. After an incubation period of 2 to 4 days, diphtheria usually presents as pharyngitis or tonsillitis. Patients are often febrile and complain of sore throat and malaise (body discomfort). The hallmark for diphtheria is the presence of an exudate or membrane that is usually on the tonsils or pharyngeal wall. The gray-white membrane is a result of the action of diphtheria toxin on the epithelium at the site of infection. Complications occur frequently with diphtheria and are usually seen during the last stage of the disease (paroxysmal stage). The most feared complications are those involving the central nervous system such as seizures, coma, or blindness. Information as to how this organism causes disease is discussed in Chapter 69. Additional specifics regarding this organism are provided in Chapter 17.

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Aug 25, 2016 | Posted by in MICROBIOLOGY | Comments Off on Upper Respiratory Tract Infections and Other Infections of the Oral Cavity and Neck

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