Orientia tsutsugamushi (Scrub Typhus)

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This page provides routine testing information for scrub typhus at Public Health Ontario (PHO). The etiological agent of scrub typhus is the intracellular bacterium Orientia tsutsugamushi.

* Copie d'impression non contrôlée. Valide uniquement le jour de l'impression : 21 nov. 2024.

Testing Indications

Testing is indicated for individuals with a history of exposure to mites in endemic areas and clinical presentation compatible with suspected scrub typhus.

Acceptance/Rejection Criteria

Requests for testing will only be accepted if the following information is provided:

Clinical history with symptom onset within the last 30 days
Exposure to Asia, the Middle East, Africa, or South America (specifically Chile or Peru)

Specimen Collection and Handling

Specimen Requirements

Test Requested	Required Requisition(s)	Specimen Type	Minimum Volume	Collection Kit
Orientia or scrub typhus serology or antibody	General Test Requisition	Serum	5.0 ml whole blood or 1.0 ml serum	Serum separator tube (SST)
Orientia or scrub typhus PCR or molecular	General Test Requisition	Whole blood	1.0 ml whole blood	EDTA tube
Orientia or scrub typhus PCR or molecular	General Test Requisition	Tissue biopsy (eschar or skin lesion)	N/A	Empty sterile container
Orientia or scrub typhus PCR or molecular	General Test Requisition	Skin swab (under eschar)	N/A	Empty sterile container

Submission and Collection Notes

Complete all fields of the General Test Requisition form including:

Clinical history (including if antibiotics administered)
Symptom onset date
Travel history
Arthropod exposure history

Label the specimen container(s) with the patient’s first and last name, date of collection, and one other unique identifier such as the patient’s date of birth or Health Card Number. Failure to provide this information may result in rejection or testing delay.

Timing of Specimen Collection

For serology, collecting both an acute serum (collected early after the onset of symptoms) and a convalescent serum (collected 2-3 weeks later) may be required for laboratory confirmation of infection.

For PCR, samples should ideally be collected prior to the initiation of antibiotic therapy, but treatment should never be withheld, if required based on the patient’s clinical status.

Limitations

Grossly haemolysed, lipemic, or contaminated specimens are unsuitable for testing.

Storage and Transport

Centrifuge serum if using SST. To prevent erroneous results due to the presence of fibrin, ensure that complete clot formation has taken place prior to centrifugation of samples.
Blood samples should be stored at 2-8°C following collection and shipped on ice packs to PHO’s laboratory as soon as possible.
Tissue samples should be stored frozen following collection and shipped on dry ice to PHO’s laboratory as soon as possible.
All clinical specimens must be shipped in accordance with the Transportation of Dangerous Goods Act.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Orientia tsutsugamushi serology is forwarded to the National Microbiology Laboratory (NML) in Winnipeg. Turnaround time for serology is up to 21 calendar days from receipt at PHO’s laboratory.

Orientia tsutsugamushi PCR is forwarded to the NML in Winnipeg. Turnaround time for PCR is up to 21 calendar days from receipt at PHO’s laboratory.

Test Methods

Method: Orientia tsutsugamushi serology is performed at NML using the commercial InBios Scrub Typhus Detect IgM and IgG assays. This duplex assay provides semi-quantitative detection of IgM and IgG antibodies to an Orientia tsutsugamushi derived recombinant antigen.

Orientia tsutsugamushi PCR is performed at NML using a laboratory-developed real-time PCR specific for the 47 kDa outer membrane protein gene of Orientia tsutsugamushi.¹

Performance: Single acute serology sensitivity is < 60% when collected within the first week of illness. IgM may become detectable 5 to 10 days following symptom onset, while IgG titres may take weeks to become detectable. Overall, IgM and IgG sensitivity is estimated at 70-100% and 58-96%, respectively, while IgM and IgG specificity is estimated at 87-100% and 92-98%, respectively. Skin tissue PCR sensitivity ranges from 78-92% and whole blood PCR sensitivity ranges from 82-86% (pre-antibiotics) to from 50-69% (post-antibiotics).^2,3,4,5,6

Limitations: Serology may be negative in the acute stage of illness. False positive IgM results may occur and should be confirmed by collecting a convalescent serology sample. A positive IgM and IgG result does not distinguish active versus remote infection unless paired sera are collected demonstrating seroconversion. The current PCR and serology assays may not detect other rare non-tsutsugamushi Orientia species (e.g. “Candidatus Orientia cholensis”).

Interpretation

For Orientia tsutsugamushi serology:

Scrub Typhus ELISA IgM Result	Scrub Typhus ELISA IgG Result	Interpretation
Non-reactive	Non-reactive	No serological evidence of scrub typhus infection. A non-reactive test result does not exclude the diagnosis of scrub typhus. If scrub typhus is suspected, submit a new specimen 2-3 weeks later for repeat (convalescent) serology.
Reactive	Non-reactive	IgM antibodies detected. False positive IgM results may occur; submit a new specimen 2-3 weeks later for repeat (convalescent) serology).
Non-reactive	Reactive	IgG antibodies detected. A positive IgG result does not distinguish active versus remote infection unless paired sera were collected demonstrating seroconversion.
Reactive	Reactive	IgM and IgG antibodies detected. A positive IgM and IgG result does not distinguish active versus remote infection unless paired sera were collected demonstrating seroconversion.

For Orientia tsutsugamushi PCR:

Scrub Typhus PCR Result	Interpretation
Negative	No evidence of O. tsutsugamushi DNA. A negative result does not exclude the diagnosis of rickettsial disease.
Positive	O. tsutsugamushi DNA detected

Reporting

Results are reported to the physician, authorized health care provider (General O. Reg 45/22, s.18) or submitter as indicated on the requisition.

References

Jiang J, TC Chan, JJ Temenak, GA Dasch, WM Ching, AL Richards. Development of a quantitative real-time polymerase chain reaction assay specific for Orientia tsutsugamushi. Am J Trop Med Hyg 2004; 70(4): 351-356.
Prakash JAJ. Scrub typhus: risks, diagnostic issues, and management challenges. Res Rep Trop Med. 2017 Aug 7;8:73-83. doi: 10.2147/RRTM.S105602.
Kim CM, Kim DM, Yun NR. Evaluation of the Diagnostic Accuracy of Antibody Assays for Patients with Scrub Typhus. J Clin Microbiol. 2021 Jun 18;59(7):e0294220. doi: 10.1128/JCM.02942-20.
Yun NR, Kim CM, Kim DY, Seo JW, Kim DM. Clinical usefulness of 16S ribosomal RNA real-time PCR for the diagnosis of scrub typhus. Sci Rep. 2021 Jul 12;11(1):14299. doi: 10.1038/s41598-021-93541-w.
Kim DM, Park G, Kim HS, Lee JY, Neupane GP, Graves S, Stenos J. Comparison of conventional, nested, and real-time quantitative PCR for diagnosis of scrub typhus. J Clin Microbiol. 2011 Feb;49(2):607-12. doi: 10.1128/JCM.01216-09. Epub 2010 Nov 10.
Kim DM, Kim HL, Park CY, Yang TY, Lee JH, Yang JT, Shim SK, Lee SH. Clinical usefulness of eschar polymerase chain reaction for the diagnosis of scrub typhus: a prospective study. Clin Infect Dis. 2006 Nov 15;43(10):1296-300. doi: 10.1086/508464.