Testing for Streptococcal Carrier State
There is no standardized test specifically designed to identify streptococcal carriers. 1
Understanding Streptococcal Carriers
- Streptococcal carriers are individuals who have Group A β-hemolytic streptococci present in their throats but show no evidence of immunologic reaction to the organism 1
- During winter and spring in temperate climates, up to 20% of asymptomatic school-aged children may be streptococcal carriers 1
- Carriers may be colonized by Group A streptococci for several months and may experience intercurrent viral pharyngitis during this period 1
- Carriers are unlikely to spread the organism to close contacts and are at low risk for developing suppurative or nonsuppurative complications (e.g., acute rheumatic fever) 1
Diagnostic Challenges
- It is difficult in clinical practice to differentiate between:
- A carrier with an intercurrent non-Group A streptococcal infection
- A patient with true acute streptococcal pharyngitis 1
- Helpful clues for differentiation include:
- Patient's age
- Season of the year
- Local epidemiology (e.g., presence of influenza or enteroviral illnesses)
- Nature of presenting signs and symptoms 1
Potential Approaches to Identify Carriers
- Performing throat cultures during asymptomatic intervals may help distinguish persistent carriage from repeated episodes of streptococcal pharyngitis 1
- Serotyping of repeated streptococcal isolates from an individual patient may assist in determining carrier status, but such studies can only be performed in specialized research laboratories 1
- The clinical significance of the number of Group A streptococcal colonies on throat culture plates is limited - while carriers tend to have fewer colonies than those with acute infection, there is too much overlap for reliable differentiation 1
Management Considerations
- Streptococcal carriers do not ordinarily require antimicrobial therapy 1
- It is more difficult to eradicate Group A streptococci from the upper respiratory tract of carriers compared to those with acute infections 1
- Many published studies showing high failure rates of penicillin therapy were likely "contaminated" with carriers 1
- For patients with multiple episodes of culture-positive pharyngitis, information about clinical response to antibiotics and presence/absence of Group A streptococci during asymptomatic intervals is helpful 1
Common Pitfalls
- Routine throat cultures after completion of antibiotic therapy for Group A streptococcal pharyngitis are not necessary unless special circumstances exist 1
- Continuous antimicrobial prophylaxis for Group A streptococcal infection is not recommended except for preventing recurrences of acute rheumatic fever 1
- Treating based solely on positive test results without considering clinical presentation can lead to unnecessary antibiotic use 2
In clinical practice, the differentiation between carrier state and acute infection often relies on clinical judgment rather than a specific laboratory test designed for this purpose.