Investigations

1st investigations to order

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Result
Test

Non-pregnant: the Centers for Disease Control and Prevention (CDC) recommends testing serum specimens collected <7 days after onset of symptoms in all symptomatic patients with possible exposure. Other acceptable specimen types include plasma, whole blood, cerebrospinal fluid (CSF), or urine.[169] If result is negative, serological tests are recommended.

Pregnant and symptomatic: CDC recommends testing paired serum and urine specimens as soon as possible up to 12 weeks after onset of symptoms in all symptomatic patients with possible exposure. Concurrent serological testing is recommended; further testing may be required if RT-PCR is positive and IgM result is negative.[168]

Pregnant and asymptomatic: CDC recommends testing paired serum and urine specimens 3 times during pregnancy (e.g., at the initial antenatal care visit, and then at 2 non-consecutive antenatal visits) in patients with ongoing possible exposure only.[168]

Pregnant women with possible exposure to Zika virus who have a fetus with antenatal ultrasound findings consistent with congenital Zika virus infection should be tested following the same recommendations for symptomatic pregnant women.[168]

Infants: CDC recommends testing in infants with clinical findings consistent with congenital Zika syndrome born to mothers with possible Zika virus exposure in pregnancy (regardless of maternal testing results), or infants without clinical findings consistent with congenital Zika syndrome who were born to mothers with laboratory evidence of possible Zika virus infection. Serum and urine should be collected from the infant in the first 2 days of life if possible (note: specimens collected within the first few weeks to months after birth still may be useful, especially in infants born in areas without risk of Zika).[2]

CSF testing can be considered in infants with clinical findings of possible congenital Zika syndrome but whose initial laboratory tests on serum and urine are negative.[2]

Availability of commercial tests depends on location.

Testing recommendations may differ between guidelines and locations.[71][176]

Result

positive for Zika virus RNA

Test
Result
Test

Non-pregnant: CDC recommends testing serum specimens collected ≥7 days after onset of symptoms in all symptomatic patients with possible exposure (or if RT-PCR on specimens collected <7 days after onset of symptoms is negative).[169] If result is positive or equivocal, plaque-reduction neutralisation testing (PRNT) is recommended (except in Puerto Rico) to confirm diagnosis.

Pregnant and symptomatic: CDC recommends testing serum specimens as soon as possible up to 12 weeks after onset of symptoms in all symptomatic patients with possible exposure. Concurrent RT-PCR is recommended; if RT-PCR is negative and serology is either positive or equivocal, PRNT is recommended (except in Puerto Rico) to confirm diagnosis.[168] May be considered >12 weeks after symptom onset; however, result should be interpreted in the context of known limitations.

Pregnant and asymptomatic: CDC no longer routinely recommends IgM testing in these patients.[168]

Pregnant women with possible exposure to Zika virus who have a fetus with antenatal ultrasound findings consistent with congenital Zika virus infection should be tested following the same recommendations for symptomatic pregnant women.[168]

Infants: CDC recommends testing in infants with clinical findings consistent with congenital Zika syndrome born to mothers with possible Zika virus exposure in pregnancy (regardless of maternal testing results), or infants without clinical findings consistent with congenital Zika syndrome who were born to mothers with laboratory evidence of possible Zika virus infection. Serum should be collected from the infant in the first 2 days of life if possible (note: specimens collected within the first few weeks to months after birth still may be useful, especially in infants born in areas without risk of Zika). A positive result (with positive RT-PCR) confirms infection. A non-negative result (with negative RT-PCR) indicates probable infection.[2]

Availability of commercial tests depends on location.

Result

positive for Zika virus antibodies; PRNT ≥10

Test
Result
Test

It is important to differentiate between Zika, dengue, and chikungunya virus infection as the three diseases can produce similar symptoms, particularly during the acute phase.

RT-PCR or serology for dengue and/or chikungunya is recommended in patients at risk of exposure with clinically compatible illness.[169][168]

The CDC recommend the following tests in people with symptoms who live in or travel to areas where there is a risk for infection with both dengue and Zika viruses: (1) symptomatic non-pregnant women - nucleic acid amplification tests (NAATs) such as RT-PCR for dengue and Zika viruses performed on serum collected in the first 7 days after symptom onset, or serological testing (IgM antibody testing for dengue and Zika viruses) on serum collected >7 days after symptom onset, or in patients with a negative NAAT result; (2) symptomatic pregnant women - simultaneous NAATs and IgM antibody testing for both dengue and Zika viruses on serum and urine specimens as soon as possible within 12 weeks of symptom onset (a positive IgM antibody test result with a negative NAAT result should be confirmed by neutralising antibody tests).[172]

Result

depends on test and organism

Investigations to consider

Test
Result
Test

Microcephaly can sometimes be diagnosed on antenatal ultrasound, especially if performed in late pregnancy. Intrauterine diagnosis of microcephaly is made when the head circumference is ≥2 standard deviations below the mean for gender and gestational age.[170]

Pregnant women with laboratory evidence of possible Zika virus infection should have serial ultrasounds every 3 to 4 weeks to monitor fetal anatomy and growth, and be referred to a specialist.[168]

In Brazil, 3 ultrasounds are recommended during low-risk pregnancies, with monthly ultrasounds recommended in pregnant women with confirmed infection.[177]

A systematic review and meta-analysis found that overall diagnostic test accuracy of ultrasound for predicting microcephaly at birth is limited as it varies with the applied cut-offs, and that it appears more accurate at detecting the absence of microcephaly rather than its presence.[178]

Result

may show microcephaly, intracranial calcifications, or brain/eye abnormalities

Test
Result
Test

If amniocentesis is performed as part of routine clinical care, RT-PCR should be performed on amniotic fluid as a positive result may indicate fetal infection.[168]

Result

positive for Zika virus RNA

Test
Result
Test

Infant’s head circumference should be measured at birth, 24 hours after birth, and then regularly during early infancy using standardised methods and compared with growth standards.[170][179]

The Centers for Disease Control and Prevention (CDC) defines definite microcephaly as head circumference at birth less than the third percentile for gestational age and gender, or head circumference less than the third percentile for age and gender within the first 2 weeks of life (if head circumference at birth is not available).[180]

The World Health Organization (WHO) defines microcephaly as a head circumference of ≥2 standard deviations below the mean for age and gender, and severe microcephaly as a head circumference of ≥3 standard deviations below the mean for age and gender. WHO Child Growth Standards or the INTERGROWTH-21 Size at Birth Standards should be used to interpret measurements.[179]

Some infants may present with craniofacial disproportion (i.e., the head appears disproportionately small relative to the face).[179]

Poor head growth with microcephaly developing after birth has been reported in a small number of patients in Brazil.[162]

CDC: measuring infant head circumference: an instructional video for healthcare providers external link opens in a new window

Result

third percentile or ≥2 standard deviations below the mean (for age and gender)

Test
Result
Test

A standard evaluation is recommended in all infants born to mothers with possible or confirmed infection, regardless of whether the infant has clinical findings consistent with congenital Zika syndrome. The evaluation should include: a comprehensive physical examination including growth parameters; developmental monitoring and screening using validated tools; vision screening; and newborn hearing screen at birth, with automated auditory brainstem response (ABR) if possible.[2]

In addition to this, infants with clinical findings consistent with congenital Zika syndrome, and infants without clinical findings born to mothers with laboratory evidence of possible Zika virus infection, should have the following investigations: head ultrasound; comprehensive ophthalmological examination by 1 month of age; and automated ABR by 1 month of age (if not already done as part of standard newborn evaluation).[2]

Infants with clinical findings consistent with congenital Zika syndrome should also have the following: referral to a development specialist, early intervention service programmes, and family support services; and consultation with infectious disease, clinical genetics, and neurology specialists, as well as any other clinical specialists based on the infant’s clinical findings (e.g., endocrinologist, lactation specialist, gastroenterologist, speech or occupational therapist, orthopaedist, physiotherapist, pulmonologist).[2]

Result

abnormalities consistent with congenital Zika virus infection

Test
Result
Test

Recommended in infants with microcephaly (or craniofacial disproportion) where Zika infection is suspected in the mother during pregnancy, or if any neurological signs/symptoms are present in the infant.[179]

Either CT or MRI can be performed; however, an MRI may provide more detail and can potentially detect other conditions.[179]

The most common feature found on CT is brain calcifications in the junction between the cortical and subcortical white matter, often with a simplified gyral pattern and predominance of pachygyria or polymicrogyria in the frontal lobes. These calcifications often resolve; therefore, the absence of calcifications should not exclude the diagnosis, and the presence of calcifications should not be consIdered a major criterion for diagnosis.[181]

Other findings include abnormalities of the corpus callosum (hypogenesis or hypoplasia), enlarged cisterna magna, ventriculomegaly, delayed myelination, and hypoplasia of the cerebellum and brainstem.[182][183]

Some infants have been found to have vision-threatening eye findings (e.g., macular and perimacular lesions, pigmentary retinopathy and atrophy, torpedo maculopathy, haemorrhagic retinopathy).[184][185][186][187][188][189] Ocular findings were seen more often in infants with smaller cephalic diameter at birth, and infants born to mothers who reported symptoms in the first trimester.[190]

Signs of congenital brain injury (e.g., subependymal cysts, lenticulostriate vasculopathy) due to Zika virus infection acquired during the third trimester of pregnancy have been reported.[161]

com.bmj.content.model.Caption@7a6140fd[Figure caption and citation for the preceding image starts]: CT scan of the head of an infant with Zika virus infection showing a clear distribution of periventricular calcificationsFrom the personal collection of Dr Geraldo Furtado, MD, MSc (used with permission) [Citation ends].

Result

may show intracranial calcifications, ventriculomegaly, cerebellar hypoplasia, callosal abnormalities, or ocular findings

Test
Result
Test

Nerve conduction studies/electromyography and CSF examination should be performed in patients with suspected Guillain-Barre syndrome if available; however, these investigations are not needed to make a clinical diagnosis and should not delay treatment.[151]

Interpretation of these studies and definitive diagnosis requires consultation with a neurologist.

Result

slowing of nerve conduction velocities; elevated CSF protein

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