eMedicine Specialties > Infectious Diseases > HEENT Infections

Pharyngitis, Bacterial

Author: Eric S Halsey, MD, Chief, Department of Infectious Diseases, Wright-Patterson Air Force Base; Assistant Professor of Medicine, Uniformed Services University of the Health Sciences; Assistant Professor of Medicine, Wright State University
Contributor Information and Disclosures

Updated: May 19, 2009

Introduction

Background

Pharyngitis, or sore throat, is often caused by infection. Common respiratory viruses account for the vast majority of cases (see Pharyngitis, Viral), and these are usually self-limited. Bacteria are also important etiologic agents, and, when identified properly, may be treated with antibacterials, resulting in decreased local symptoms and prevention of serious sequelae.

The most common and important bacterial cause of pharyngitis is Streptococcus pyogenes. When suspected, bacterial pharyngitis can be confirmed with routine diagnostic tests and treated with various antibiotics. If left untreated, S pyogenes pharyngitis may lead to local and distant complications. To a lesser extent, bacteria other than S pyogenes are known to cause pharyngitis, and these are discussed in Causes.

Pathophysiology

Beta-hemolytic streptococci have the ability to cause large zones of hemolysis on blood agar, aiding in microbiological identification.¹ Lancefield antigens, carbohydrates in the cell wall, provide further differentiation of streptococci. S pyogenes, which contains group A antigens and displays beta-hemolysis, is the most common species referred to as a group A beta-hemolytic streptococci (GABHS). Streptococcus dysgalactiae subspecies equisimilis and some species from the Streptococcus anginosus group may share laboratory characteristics with S pyogenes but do not commonly cause human disease.

Perhaps the most important virulence factor of GABHS is the M protein. This protein, located peripherally on the cell wall, is required for invasive infection. T cells exposed to this M protein are postulated to cross-react with similar epitopes on human cardiac myosin and laminin, contributing to the pathogenesis of rheumatic heart disease.² This protein provides a potential target for a GABHS vaccine, although successful widespread implementation of such a vaccine remains elusive.³ More than 100 M-protein serotypes have been described. Although individuals often develop lifelong immunity to one serotype, re-infection with a different serotype may cause disease.

GABHS contains a hyaluronic acid capsule, which also plays an important role in infection.⁴ Bacteria that produce large quantities of this capsule exhibit a characteristic mucoid appearance on blood agar and may be more virulent.

Certain GABHS exotoxins act as superantigens by up-regulating T cells.⁵ These superantigens can prompt a release of proinflammatory cytokines and may synergize with lipopolysaccharide. It has been speculated that these superantigens evade the pharyngeal immune response, resulting in proliferation of GABHS while permitting immune-mediated elimination of commensal organisms.

Adhesins enable GABHS attachment at sites such as the pharynx. This attachment allows for colonization and competition with normal host flora.

Some strains produce erythrogenic toxins, which cause the rash of scarlet fever in susceptible hosts.

GABHS is spread from person to person through large droplet nuclei.⁶ Consequently, close quarters (eg, barracks, daycares, dormitories) facilitate transmission. In temperate regions, the prevalence of GABHS infection increases in the colder months, presumably because of the tendency of people to congregate indoors. Spread within families is common. The risk of acquiring GABHS from an infected family member is 40%, and nearly one in four of infected individuals eventually exhibit symptoms. Twenty-four hours after appropriate antibiotics are initiated, the patient is no longer considered contagious.

Case reports and in vitro studies have speculated that toothbrushes, orthodontic appliances, and pets may carry and facilitate spread of GABHS,^7,8 although these claims have not been validated by rigorous in vivo investigation.⁹

GABHS is also a common cause of erysipelas, cellulitis, and necrotizing fasciitis and has been reported as a cause of pneumonia, toxic shock syndrome, and lymphangitis. The vast majority of these manifestations do not occur in the setting of pharyngitis.

Frequency

United States

Acute pharyngitis accounts for approximately 12 million annual ambulatory care visits in the United States. It ranks within the top 20 most-common primary diagnosis groups.¹⁰

International

An estimated 616 million cases of GABHS pharyngitis occur annually worldwide.¹¹ Rheumatic heart disease, which may be a consequence of GABHS pharyngitis, is estimated to cause about 6 million years of life lost annually. The burden of rheumatic heart disease disproportionately affects populations from developing countries. In terms of estimated global mortality, GABHS is one of the top 10 pathogens, behind HIV infection and malaria and ahead of tetanus and pertussis.

Mortality/Morbidity

Although GABHS pharyngitis is usually a self-limited entity, on average, a single episode in a child results in 1.9 days absence from school and a parent missing 1.8 days from work to care for the child.¹² Children with GABHS pharyngitis experience symptoms for an average of 4.5 days.

In addition to symptoms localized to the oropharynx, GABHS pharyngitis may also cause the following suppurative and nonsuppurative complications:

• Invasion of nearby structures may cause suppurative complications such as otitis media, sinusitis, peritonsillar abscess, retropharyngeal abscess, and cervical adenitis.
• Nonsuppurative complications of bacterial pharyngitis include rheumatic heart disease and poststreptococcal glomerulonephritis. These entities are discussed in Complications.

Race

GABHS pharyngitis affects all races.

Sex

GABHS pharyngitis has no sexual predilection.

Age

GABHS pharyngitis is most common in individuals aged 5-15 years, although both infants and adults may also acquire the disease. (For more information on pharyngitis in children, see the article Pharyngitis in eMedicine's Pediatric: General Medicine volume.)

Clinical

History

The signs and symptoms listed below may be seen with many non-GABHS etiologies. Furthermore, individuals with GABHS pharyngitis may have only a few or mild features listed. Conjunctivitis, cough, hoarseness, coryza, diarrhea, anterior stomatitis, discrete ulcerative lesions, and a viral exanthem are all more consistent with an etiology other than GABHS.

• Sore throat, usually with sudden onset
• Odynophagia
• Headache
• Nausea, vomiting, and abdominal pain

Physical

• Fever
• Tonsillopharyngeal erythema
• Exudates (patchy and discrete)
• Beefy red swollen uvula
• Lymphadenopathy (tender anterior cervical nodes)
• Petechiae on the palate
• Scarlatiniform rash (In susceptible hosts, this usually manifests within the first two days of symptoms and causes a finely papular, blanching, and erythematous rash. The neck is often first affected and then spreads along the trunk and limbs. Resolution, often at 3-4 days, occurs in roughly the same order of appearance and often results in desquamation of the involved areas.)

Predictive models can help determine the likelihood of GABHS pharyngitis based on the presence of fever, swollen tender anterior cervical lymph nodes, and tonsillar exudates and the absence of cough. Scores have been used to distinguish which patients merit further laboratory evaluation or treatment. The use of such clinical algorithms has been the source of much debate.^13,14

Causes

• Viruses cause the vast majority of pharyngitis cases. Common agents include coronavirus, rhinovirus, adenovirus, parainfluenza, influenza, Epstein-Barr virus, cytomegalovirus, and HIV.
• GABHS accounts for 15%-30% of pharyngitis cases in children and 5%-10% of cases in adults.¹³
• The following are bacteria other than GABHS that may cause pharyngitis:
  • Group C and G streptococci: Like GABHS, these pathogenic bacteria cause beta-hemolysis, form large colonies, and produce an M protein, yet neither are detected with rapid antigen detection tests (RADTs). Pharyngitis caused by either of these non-GABHS streptococci have a clinical presentation similar to that of GABHS pharyngitis and should be considered in patients with worsening symptoms and an initial negative RADT result. Diagnosis can be achieved with a normal bacterial throat culture and identification based on Lancefield antigens.¹⁵ These bacteria are an uncommon cause of acute pharyngitis in pediatric patients.¹⁶
  • Arcanobacterium haemolyticum: This gram-positive rod accounts for between 0.5% and 3% of pharyngitis cases.¹⁷ Clinical manifestations are similar to those of GABHS pharyngitis, although about half of patients with A haemolyticum pharyngitis develop a rash, which typically starts on the extensor surfaces; spares the palms, soles, and head; and moves centrally to involve the trunk with a maculopapular or scarlatiniform appearance. A haemolyticum exhibits variable susceptibility to penicillin and is identified more easily on human or rabbit blood agar than on sheep agar, the media traditionally used to identify GABHS.
  • Neisseria gonorrhoeae: Infection with this pathogen is associated with oral-genital contact and is often asymptomatic. N gonorrhoeae may be identified using chocolate or Thayer-Martin agar.¹⁸ Nucleic acid amplification tests from throat rinses appear to be a promising alternative.¹⁹ Because of increasing rates of fluoroquinolone resistance, ceftriaxone is now the only recommended option for treatment of pharyngeal gonorrhea.²⁰ Treatment aimed at Chlamydia trachomatis is also recommended, since co-infection is common.
  • Mycoplasma pneumoniae: This atypical bacterium is increasingly being identified as an etiologic agent of pharyngitis.²¹ M pneumoniae pharyngitis may be associated with pulmonary findings.²²
  • Yersinia species: Both Yersinia enterocolitica and Yersinia pestis may cause disease. Pharyngeal plague has been linked to the consumption of camel meat.²³
  • Chlamydia trachomatis and Chlamydophila pneumoniae: Both of these organisms are rare causes of pharyngitis.^21,19
  • Corynebacterium diphtheriae: Toxigenic strains of this gram-positive bacillus are common causes of croup.¹⁷ Young patients with C diphtheriae pharyngitis often exhibit inspiratory stridor, sternal retraction, and a barking cough. In severe cases, a membrane formation may impair breathing. The incidence of C diphtheriae pharyngitis in developed countries is low because of high immunization rates.

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