California Serogroup Serology and PCR

Testing Indications

California serogroup (CSG) viruses are mosquito-borne pathogens that may cause encephalitis in humans. CSG viruses circulate across Canada and the United States. Clinical cases as well as seroprevalence rates of 20-30% have been documented from coast to coast including northern regions of the country such as the Yukon and North West Territories. It is recommended that CSG viruses, and other arboviruses present in Ontario (e.g., West Nile, Powassan, Eastern equine encephalitis viruses) be part of the differential for neurological case investigations that occur during the active mosquito season. The NML currently tests for the two most prevalent CSG viruses in Ontario and Canada, Jamestown Canyon and Snowshoe Hare viruses.¹

Note: La Crosse virus, the most commonly documented CSG virus in the United States, is not present in Canada.

Timing of Specimen Collection

The following paired samples are accepted for CSG serology:

1. Paired serum samples (acute and convalescent) collected 2-3 weeks apart from patients with clinical illness
2. CSF paired with single serum from patients with clinical illness.

Limitations

Persistent IgM and the high seroprevalence associated with CSG viruses in the Canadian population makes it difficult to differentiate recent from past infections from a single serum specimen, thus the need for paired sera and/or CSF.

PCR is not recommended for CSG viruses as it is not a sensitive test for CSG viruses, unless collected within 5 days of neurological onset during active mosquito season. NML will determine if molecular testing is feasible after serological testing is complete.

Preparation Prior to Transport

Specimens should be stored at 2-8°C or frozen following collection. Ship refrigerated samples on ice packs and frozen samples on dry ice.

Special Instructions

Complete all fields of the General Test Requisition, including:

• Requesting health care provider (CPSO number)
• Complete mailing address
• Telephone and fax number
• Patient’s full name, date of birth, and health card number where applicable (must match specimen label)
• Test(s) requested and indication for testing
• Travel history (mandatory)
• Exposure history and details (if applicable)
• Clinical information including symptom onset date (clinical presentation, risk factors, exposure history) [mandatory]
• Specimen type(s) and collection

Failure to complete all requisition fields appropriately may result in rejection or testing delay.

Test Frequency and Turnaround Time (TAT)

The Turnaround Time (TAT) for IgM Enzyme Linked Immunosorbent Assay (ELISA) is 14 days from receipt at NML.

The TAT for the confirmatory Plaque Reduction Neutralization Test (PRNT) is 28 days from receipt at NML.

RT-PCR (if performed) is 14 days following the ELISA.

Reporting

Results are reported to the ordering physician or health care provider as indicated on the requisition.

Positive CSG results for encephalitis cases are reported to the Medical Officer of Health as per the Ontario Health Protection and Promotion Act.

Screening test: IgM ELISA only ; IgG ELISA not performed.

Confirmatory test : PRNT

Optional test: molecular detection by PCR

Algorithm

Submitted samples will first be analyzed by the IgM ELISA to determine if the patient has developed antibodies. IgM-reactive specimens will undergo PRNT confirmation.
Note: IgG serology is not available/not performed at NML.

Samples that are reactive will be further analyzed for the presence of neutralizing antibodies.

Samples that are ELISA non-reactive (negative) will not be tested by PRNT.

PCR testing will be considered on a case-by-case basis.