Practical Clinical Microbiology and Infectious Diseases

A Hands-On Guide

Firza Alexander Gronthoud, Firza Alexander Gronthoud

• Éditeur: CRC Press
• Année: 2020
• ISBN:
  9781351760041
• Édition: 1
• Sujet: Medicine
• Sous-sujet: Medical Theory, Practice & Reference

This book offers practical tips and essential guidance for trainees and specialists in clinical microbiology and infectious diseases and healthcare professionals interested in infection management to put theoretical knowledge into daily practice. Using common clinical situations and problems as a guide, the handbook is intended to support the healthcare professional from interpretation of laboratory results to consultation and infection control.

Key Features

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• Concisely covers the critical clinical microbiology and infectious disease topics, with an emphasis on translating theoretical knowledge into clinical practice
• Provides practical guidance and solutions to commonly encountered issues and scenarios
• Presented in an accessible format to rapidly aid the clinician in day-to-day practice

Section IV

Special Problems

4.1

Acute Streptococcal Pharyngitis

Firza Alexander Gronthoud

Clinical Considerations

Streptococcus pyogenes or Group A Streptococcus (GAS)

GAS is the main cause of bacterial pharyngitis and causes up to 30% of all cases of acute pharyngitis in children and up to 10% in adults. Patients with pharyngitis spread GAS via the respiratory route. GAS pharyngitis has an incubation period of 2–5 days and symptoms can last up to 5 days. Antimicrobial therapy reduces duration and severity of symptoms by 1–2 days (when begun within 48 hours of illness). Its main goal is to prevent transmission to others and reduce risk of rheumatic fever. Some guidelines recommend routine treatment of GAS pharyngitis. GAS bacteraemia is rarely associated with uncomplicated pharyngitis or nonsuppurative complications of pharyngitis.

Risk of Poststreptococcal Complications

The rate of poststreptococcal complications is generally low. Risk factors are:

•Individuals at increased risk of severe infections such as the immunocompromised.

•Valvular heart disease

•History of rheumatic fever

•Of note, pharyngitis in male patients aged 21–40 years who are smokers is more frequently complicated by peritonsillar abscess

Complications of Streptococcal Pharyngitis

Complications of streptococcal pharyngitis can result from extension of infection beyond the oropharynx, termed suppurative complications, or as immune phenomena, termed nonsuppurative complications.

Nonsuppurative Complications of GAS Tonsillopharyngitis

•Acute rheumatic fever (ARF): Develops 2–3 weeks after initial pharyngitis. Clinical manifestations are arthritis, carditis, chorea, subcutaneous nodules and erythema marginatum. Low incidence in industrialized countries.

•Poststreptococcal reactive arthritis (PSRA): Occurs within 1 month following pharyngitis and involves ≥1 joint.

•Scarlet fever or ‘scarlatina’: Diffuse erythematous eruption occurring in association with pharyngitis and caused by skin reactivity to pyrogenic exotoxin produced by GAS.

•Streptococcal toxic shock syndrome: See Chapter 4.33.

•Acute glomerulonephritis: Infection with specific nephritogenic strains of GAS. Ranges from microscopic haematuria to acute nephritic syndrome. Renal failure can occur. In contrast to PSRA, only glomerulonephritis is linked with skin infections due to GAS.

•Paediatric autoimmune neuropsychiatric disorder associated with group A streptococci (PANDAS): Development of obsessive-compulsive disorder or tic disorders following GAS infection.

Clinical Pearl

•The rash of scarlet fever is a diffuse blanchable erythema. Raised papules give a rough texture like ‘sandpaper’.

•Starting in the groin and armpits, followed by rapid expansion to the trunk and extremities with sparing of palms and soles before desquamation sets in.

•Accompanied by circumoral pallor and a strawberry tongue.

•Pastia’s lines or Pastia’s signs appear before the rash and persist after desquamation. These are confluent petechiae in a linear pattern found in skin creases, i.e. groin, axilla, neck folds.

•Children may return to school or day care 24 hours after initiation of antibiotics.

Suppurative Complications of GAS

•Otitis media: GAS causes a minority of all cases of acute otitis media (AOM), but incidence of AOM due to GAS is increased during the winter months

•Sinusitis

•Peritonsillar abscess, also called quinsy: Often polymicrobial flora involved

Prevention of Transmission and Complications

Penicillin decreases risk of rheumatic fever by about two-thirds with greatest risk reduction in children 5–15 years living in geographical areas with highest incidence of rheumatic fever. The effect of penicillin on risk reduction of other nonsuppurative complications is not well known.

GAS can spread among close contacts, leading to clusters of cases and recurrent infections in households or other close contact settings. The rate of GAS transmission from an infectious case to close contacts is estimated to be between 5% and 50%. Antibiotics eliminate GAS from the oropharynx in about 80%–90% of cases after 24 hours of therapy. About half of patients with untreated streptococcal pharyngitis are shedding GAS in the oropharynx for 3–4 weeks after resolution of symptoms.

Clinical Approach

The diagnosis of GAS pharyngitis is supported by a positive microbiologic test (throat culture or rapid antigen detection test [RADT] for GAS), symptoms consistent with pharyngitis and either a negative viral respiratory PCR or absence of signs and symptoms of viral infections (e.g. coryza, conjunctivitis, cough, hoarseness, anterior stomatitis, discrete ulcerative lesions or vesicles, diarrhoea).

The likelihood of a GAS pharyngitis can be predicted with the Centor or FeverPAIN criteria. Criteria are less sensitive in young children who often have aspecific symptoms (see Table 4.1.2).

Whom to Test

A throat swab or rapid test is indicated if there is an acute tonsillopharyngitis or scarlatiniform rash and viral causes have been excluded (Table 4.1.1).

Table 4.1.1 ...