Zika virus: sample testing advice
Guidance on who to test for Zika virus infection and which samples to collect.
Access to Zika virus testing services
This guidance on the laboratory diagnosis of Zika virus infection is intended for healthcare professionals in the UK. Patients concerned about possible Zika virus infection should consult an appropriate healthcare professional, for example their GP, in the first instance.
Health professionals wishing to discuss a possible case, or to ascertain local arrangements, should contact a local Infection specialist (such as a consultant in infectious diseases, microbiology or virology).
NHS testing for Zika virus is available only through the Rare and Imported Pathogens Laboratory (RIPL) at PHE Porton. RIPL provides medical and laboratory specialist services to the NHS and other healthcare providers, covering advice and diagnosis of a wide range of unusual bacterial and viral infections, including Zika virus infection.
Investigation of asymptomatic returned travellers
The Zika virus testing service is currently not available for individuals who have had no symptoms suggestive of Zika infection. This includes:
- asymptomatic pregnant women who have travelled from Zika-affected countries
- asymptomatic returned male travellers whose partners are currently pregnant
- asymptomatic returned male and female travellers who are trying to conceive
These individuals should be advised to follow PHE guidance on prevention of pregnancy and avoidance of sexual transmission as appropriate.
This situation will be kept under review. For this reason, service users are strongly advised to continuously refer back to this on-line guidance (which will be kept up to date) and not rely on printed copies.
Investigation of patients with current or previous symptoms
Clinicians should consider Zika virus infection for:
- any patient who has, or has had, a rash illness or fever, or other symptoms suggestive of Zika virus infection, that began whilst in any country with active Zika virus transmission, or within 2 weeks of leaving that country
- any patient presenting with typical Zika-like symptoms apparently due to sexual transmission in the UK; that is, there is no history of travel or the symptoms began more than 2 weeks after travel to a Zika-affected country, and their sexual partner (especially if male) had travelled within the last 8 weeks from a country with active Zika virus transmission
When assessing patients presenting with acute symptoms, doctors should also consider other travel-associated infections in the differential diagnosis, including:
- dengue and chikungunya virus infections
- common infections not associated with travel
- non-infectious diseases
Clinicians should also read PHE guidance on rash in pregnancy for other possible causes of a rash.
Which samples to collect from patients
Submit samples with the RIPL request form, as explained below. Samples submitted with inadequately completed forms may not be tested.
|Returned traveller (or UK visitor) category (1)||Current symptoms consistent with Zika infection (2)||Previous symptoms consistent with Zika infection (2) (none now)||Never had symptoms suggestive of Zika infection|
|Pregnant woman or male partner of pregnant woman||Serum (3,4), EDTA plasma and urine||Serum (3,4). Also urine if within 21 days since symptom onset||No testing. Advise on prevention of sexual transmission|
|Other returned traveller/UK visitor not in above group (5)||Serum (3) and EDTA plasma only||Serum only (3)||No testing. Advise on prevention of pregnancy and sexual transmission|
- Zika virus infection should also be considered in any non-traveller whose sexual partner has travelled within the last 8 weeks from a country with active Zika virus transmission, particularly if this partner is male
- symptoms suggestive of Zika virus infection that began whilst in a country with active Zika virus transmission or within 2 weeks of leaving
- an acute serum sample should be obtained and submitted promptly. However, a follow-up sample may be required subsequently; see Interpretation of Zika virus test results
- for pregnant women, it is particularly important to consider alternative diagnoses
- this category of returned traveller includes men and women who are trying to conceive
Completion of RIPL Request Forms
Diagnostic samples must be submitted with a completed request form providing details of the patient’s travel history, symptoms and, if relevant, pregnancy. There is no need to send a separate form with each sample. Samples submitted with inadequately completed forms may not be tested.
The standard RIPL request form (P1) should always be used. For any returning traveller who is significantly unwell with acute febrile illness or who requires admission to hospital, provided detailed information about travel and symptoms is included, RIPL will perform Zika testing in addition to the appropriate geographic panel of PCR and serology tests.
Ideally, the RIPL request form should be printed out and completed (except for the Sender’s Information at the top) by the clinician who sees the patient. Send the request to the local laboratory with the clinical samples along with a local laboratory request form, whether this is paper or electronic.
The local laboratory should complete the Sender’s Information on the RIPL request form and then forward the completed form and samples to RIPL. However, local arrangements may vary, so clinicians are advised to liaise with their local laboratory first, before sending samples.
Standard sample types for routine Zika virus testing
Where serum is indicated in the table above, clinicians should submit a clotted blood sample (“plain” or “serum separator gel” tube) to their local laboratory. The local laboratory should submit a minimum of 0.5 mL serum to RIPL.
Where EDTA plasma is indicated in the table above, clinicians should submit an EDTA blood sample to their local laboratory. The local laboratory should forward a minimum of 0.5 mL EDTA plasma to RIPL.
Where urine is indicated in the table above, clinicians should submit urine – 5 mL is sufficient (minimum volume 1 mL) – in a Universal tube (without any preservative) to their local laboratory for forwarding to RIPL.
Other samples (including obstetric and neonatal) suitable for Zika virus testing
Semen can be tested for Zika RNA, but only if prior arrangement with RIPL has been made. Returned male travellers with current or previous symptoms should be investigated as indicated in the table above in the first instance.
A local infection specialist or senior member of the obstetric team must contact RIPL to discuss the case, before sending samples in any of the following scenarios:
Any case where amniocentesis (with or without cordocentesis) is performed for the investigation of a returned female traveller who is pregnant and who has an abnormal fetal ultrasound scan: maternal blood samples may be required for testing in addition to amniotic fluid.
Termination of pregnancy
Any case where termination of pregnancy is performed for known or presumptive congenital Zika: appropriate samples for diagnostic testing will include maternal serum, placenta, cord tissue and fetal (brain) tissue.
Miscarriage or stillbirth
Any case of miscarriage or stillbirth in a woman with known or possible Zika infection (having travelled to a country with active Zika virus transmission earlier in the pregnancy): appropriate samples for diagnostic testing will include maternal serum, placenta, cord tissue and fetal (brain) tissue.
Anticipated live delivery following known maternal Zika infection
The pregnancy of any woman with laboratory diagnosed Zika infection should be followed up in a Fetal Medicine Unit.
Whether antenatal fetal ultrasound scans have been normal or not, contact RIPL a few weeks before the anticipated live delivery to make arrangements to submit appropriate diagnostic samples for Zika virus testing. These will include placenta, cord tissue, neonatal serum, contemporaneous maternal serum, and neonatal urine. Neonatal CSF will only be appropriate if a lumbar puncture is clinically indicated.
Live delivery following undiagnosed Zika-like maternal illness
Any neonate delivered to a woman who travelled to a country with active Zika virus transmission earlier in the pregnancy and who had an illness that might have been Zika but who was not subsequently tested for Zika antibodies (even if Zika PCR tests performed in the acute phase were negative): appropriate samples for diagnostic testing will be advised on a case-by-case basis.
Note that no Zika virus testing will be required for a normal neonate born to a woman who travelled to a country with active Zika virus transmission earlier in her pregnancy but who either:
- had a negative Zika antibody test 4 weeks or more after her last possible exposure to Zika virus, or
- had no symptoms suggestive of Zika virus infection during travel or within 2 weeks of leaving and who did not have an antenatal Zika virus antibody test performed; if maternal testing for Zika antibodies was not performed antenatally, it is not necessary to perform it postnatally
Zika virus laboratory tests available at RIPL
PCR testing for detection of Zika virus RNA
- the in-house real-time PCR used at RIPL is based on published assays; it is considered developmental in that the formal PHE technical validation process has not yet been completed and is on-going
- the assay can be performed on blood (EDTA plasma is preferred), urine, saliva (mouth swabs), semen, amniotic fluid and tissue such as placenta or umbilical cord (see Other samples suitable for Zika virus testing)
Positive results are always telephoned to the referring laboratory and clinical significance discussed.
- Zika virus PCRs are performed daily, Monday to Friday, at RIPL so results are typically reported within 4 working days of sample receipt
- the cost of testing is as indicated for any real-time PCR in the RIPL User Manual. Note that where both serology and PCR are performed on a patient’s sample(s), as is usually required, the total charge will be limited to the RIPL panel flat fee
Serological testing for the detection of Zika antibodies
- tests for Zika IgG and IgM currently in use at RIPL are commercial ELISAs that have undergone technical validation at RIPL. Further in-service assay evaluation is ongoing
- the preferred sample for serological testing is serum
Positive results are always telephoned to the referring laboratory and likely clinical significance discussed.
- Zika virus antibody tests are performed 3 to 4 times per week at RIPL and results are usually reported within 7 working days of sample receipt
- the cost of testing is as indicated for any serology assay in the RIPL User Manual. Note that where both serology and PCR are performed on a patient’s sample(s), as is usually required, the total charge will be limited to the RIPL panel flat fee
Interpretation of Zika virus test results
Detection of Zika virus RNA in any sample is diagnostic of infection with this virus. If Zika virus RNA is not detected in a patient’s samples, this does not exclude previous infection with this virus.
Detection of Zika virus IgM, with or without Zika virus IgG, in a serum sample from an individual who has had recent symptoms, will usually indicate recent Zika virus infection.
Detection of Zika virus IgG, with or without IgM, in a serum sample from an individual who has had recent symptoms, will usually be consistent with recent Zika virus infection. This is because Zika virus IgM is often not detectable in individuals who have previously been exposed to other flavivirus antigens, including yellow fever vaccination.
If Zika virus antibodies are not detected in a serum sample collected at least 2 weeks after the onset of an acute viral illness featuring fever, rash, arthralgia or conjunctivitis in a pregnant woman, appropriate investigations for alternative causes including parvovirus, rubella, CMV, dengue and chikungunya infections must be carried out, if not already performed. If no firm diagnosis is made, the patient should be individually discussed with a local Infection specialist and contact with RIPL for further advice considered.
If Zika virus antibodies are not detected in a serum sample collected 4 or more weeks* after the last possible travel-associated or sexual exposure, then recent Zika virus infection can be excluded.
Therefore, pregnant women with negative antibody results for such samples do not require further extra fetal ultrasound follow-up, unless there are additional concerns.
*This period of 4 or more weeks is derived by adding together 14 days, representing the estimated upper limit of the incubation period for Zika virus, and a further 14 days representing a maximum time for the appearance of Zika antibodies after symptom onset (although available evidence indicates that antibodies usually appear much earlier than this).
RIPL Zika registrar
01980 619 659. Service available 9am to 5pm, Monday to Friday.
Main RIPL number
01980 612 348. Service available 9am to 5pm, Monday to Friday.
Imported Fever Service
0844 77 88 990. This service is available, 24 hours a day, 7 days a week, for urgent discussion of any acutely unwell febrile patient in whom severe travel-associated infection is suspected.
Testing laboratory address
Rare and Imported Pathogens Laboratory
Manor Farm Road
DX 6930400, Salisbury 92 SP
Published: 23 March 2016
Updated: 5 August 2016
- Revised substantially to reflect the use of serological testing.
- Updated symptom list.
- Updated Zika testing advice.
- First published.