Table V-3.

Laboratory Diagnosis of Pharyngitis

Etiological Agents	Diagnostic Procedures	Optimum Specimens	Transport Issues; Optimal Transport Time
Bacterial
Streptococcus pyogenes	Rapid direct antigen test (followed by a secondary test if negative)a	Dual pharyngeal swab	Swab transport device, RT, 2 h
	Direct nucleic acid amplification test (NAAT)b	Pharyngeal swab	Swab transport device, RT, 2 h
	Nucleic acid probe testsb	Pharyngeal swab
Groups C and G β-hemolytic streptococcic	Throat culture and antigen tests on isolates for Groups C and G streptococci	Pharyngeal swab	Swab transport device, RT, 2 h
Arcanobacterium haemolyticumd	Throat culture for A. haemolyticum	Pharyngeal swab	Swab transport device, RT, 2 h
Neisseria gonorrhoeaed	Throat culture for N. gonnorrhoeae	Pharyngeal swab	Swab transport device, RT, 2 h
Corynebacterium diphtheriaed	Methylene blue stain C. diphtheriae culture	Pseudomembrane	Sterile container, RT, immediately
Fusobacterium necrophorum	Anaerobic incubation. A selective medium is available	Pharyngeal swab	Anaerobic swab transport, RT, 2 h
Viral
Epstein-Barr virus (EBV)	Monospot teste	5 mL serum	Clot tube, RT, 2 h
	EBV serology
Herpes Simplex virus (HSV) [usually Type 1]	Direct detection testf	Swab of pharyngeal lesion	Swab transport device, RT, 2 h
	Culturef
	HSV IgG and IgM serologyg	5 mL serum	Clot tube, RT, 2 h
Cytomegalovirus (CMV)	CMV IgM serology	5 mL serum	Clot tube, RT, 2 h
Human immunodeficiency virus (HIV)	(see XIV Viral Syndrome)

Abbreviations: IgG, immunoglobulin G; IgM, immunoglobulin M; NAAT, nucleic acid amplification test; RT, room temperature.

^a A rapid antigen test for Streptococcus pyogenes may be performed at the point-of-care by healthcare personnel or transported to the laboratory for performance of the test. There are numerous commercially available direct antigen tests. These vary in terms of sensitivity and ease of use; the specific test employed will dictate the swab transport system used. In pediatric patients, if the direct antigen test is negative, and if the direct antigen test is known to have a sensitivity of <80%, a second throat swab should be examined by a more sensitive direct NAAT or by culture as a means of arbitrating possible false negative direct antigen test results [78]. This secondary testing is usually unnecessary in adults [79]. A convenient means of facilitating this two-step algorithm of testing for Streptococcus pyogenes in pediatric patients is to collect a dual swab initially, recognizing that the second swab will be discarded if the direct antigen test is positive.

^b Direct NAATs for Streptococcus pyogenes are more sensitive than direct antigen tests and, as a result, negative direct NAAT results do not have to be arbitrated by a secondary test. The swab transport device should be compatible with the NAAT used. Nucleic acid probe tests are usually performed on enriched broth cultures, thus requiring longer turnaround times.

^c Detection of Groups C and G β-hemolytic streptococci is accomplished by throat culture in those patients in whom there exists a concern for an etiologic role for these organisms. Only large colony types are identified, as tiny colonies demonstrating groups C and G antigens are in the S. anginosus (“S. milleri”) group. Check with the laboratory to determine if these are routinely looked for.

^d Arcanobacterium haemolyticum, Neisseria gonorrhoeae and Corynebacterium diphtheriae only cause pharyngitis in restricted epidemiologic settings. The laboratory will not routinely attempt to recover these organisms from throat swab specimens. If a clinical suspicion exists for one of these pathogens, the laboratory should be notified so that appropriate measures can be applied to aid in their detection.

^e If the Monospot test is positive, it may be considered diagnostic for EBV infection. Up to 10% of Monospot tests are, however, falsely negative. False negative Monospot tests are encountered most often in younger children. In a patient with a strong clinical suspicion for EBV infection and a negative Monospot test, a definitive diagnosis can be achieved with EBV-specific serologic testing. Such testing can be performed on the same sample that yielded a negative Monospot test. Alternatively, the Monospot test can be repeated on a serum specimen obtained 7–10 days later at which time, if the patient had EBV infection, the Monospot is more likely to be positive.

^f Probable cause of pharyngitis only in immumocompromised patients. Numerous rapid tests based on detecting HSV-specific antigen (by DFA) directly in clinical material have been developed; however the nonspecific stain Tzanck test is very insensitive and not recommended. A swab should be used to aggressively collect material from the base of multiple pharyngeal lesions and then placed in a swab transport device that is compatible with the test to be performed. Culture may be useful in immunocompromised patients.

^g The serologic test should distinguish between IgG and IgM. Depending on the age of the patient and the specific serologic assay used, in the face of a compatible illness, a single HSV-specific IgG level may be considered presumptive evidence of HSV infection. The presence of HSV-specific IgM may be considered diagnostic.