Viral Cultures in the NICU

 

Viral cultures are frequently indicated for babies with signs and symptoms compatible with viral infection (TORCH). These include culture negative sepsis and meningitis, liver enlargement and dysfunction, seizures and unexplained rashes or intra cranial lesion, thrombocytopenia and hematologic anomalies among other signs. Rather than just order “viral cultures” it is important to specify the organism being considered and obtain the correct specimen.

CMV

CMV Ag testing and culture from urine (method of choice): Send urine undiluted (not in culture media!) in sterile container (just like urine culture). Can be bag urine, should be refrigerated if not send to lab within the next hour (e.g. at MRH keep in fridge until Monday morning or better obtain overnight to be send Monday morning). For all other viral cultures (pretty much anything that goes on a swab), viral transport media is advised.

Proof of congenital infection requires isolation of CMV from urine, stool, respiratory tract secretions, or CSF obtained within 3 weeks of birth. Usually urine collected by bag is the material of choice and should be send undiluted and not in culture media. If not processed immediately, it should be kept in the refrigerator at 4C.

CMV PCR

Very sensitive test for congenital or perinatal CMV, almost any sample, best established for blood. Alternatively antigenemia test. Both, antigenemia test and quantitative PCR give you titers that can be followed.

HSV

HSV (and other) surface cultures: If conjunctivae, nasopharynx, rectum etc. cultures are sent for colonization screen, do not send separate cultures but combine all in one (can use same swab). This increases culture yield and significantly reduces costs. Unless of course you are specifically interested in a certain site but the site does not matter in a typical HSV colonization screen).

HSV PCR

PCR often can detect HSV DNA in CSF from patients with HSV encephalitis and is the diagnostic method of choice. No particular media is necessary, just an extra tube of CSF to be send for PCR. The same is true for entervirus.

Toxo

For Toxo you could send IGM and IgG testing from blood, however the best and most definitive testing is done in the Toxo reference lab at Palo Alto (see www.pamf.org/serology/).

Enterovirus

Isolation of enterovirus in cell culture is the standard diagnostic method. In general, stool, rectal swab, and throat specimens produce the highest yield, but enterovirus may be recovered from urine and blood during the acute illness and from CSF when meningitis is present. Many group A coxsackieviruses grow poorly or not at all in vitro. Therefore PC for detection of enterovirus RNA is available at least for CSF specimens. PCR is more rapid and more sensitive than cell culture and can detect all enterovirus, including enteroviruses that are difficult to culture, but lacks the ability to further characterize according to type.

Parvo

If Parvovirus B19 infection occurs during pregnancy, the overall risk of fetal infection is 30% to 50%. Only 10-15% % of fetal infections result in symptomatic disease. Gestation influences fetal outcome because fetal loss occurs in about 15% of women infected prior to 20 weeks’ gestation compared with less than 2% of women infected after 20 weeks’ gestation.

If a pregnant woman is exposed to suspected or confirmed B19 infection, her serum should be tested for parvovirus B19 IgG and IgM antibody as soon as possible after the exposure. The presence of IgG antibody at this point in time (ie, shortly after exposure) indicates preexisting immunity, and no further testing is required. Negative IgG and IgM serologies indicate serosusceptibility, and both tests should be repeated in 3 to 4 weeks. The presence of B19-specific IgM antibody in either serum sample indicates recent infection. Any pregnant woman who has clinical or laboratory evidence of recent infection needs to be monitored for possible fetal involvement.

In the baby, detection of Parvovirus DNA by DNA hybridization techniques or by PCR are the best option. These techniques work for blood, amniotic fluid and any tissue (e.g. placenta, bone marrow, heart, and liver). However, because B19 DNA can be detected by PCR for up to 6 to 9 months following acute infection, a positive B19 PCR test does not necessarily indicate acute infection in older infants. The virus does not grow in standard cell cultures, so viral cultures are not useful.

Ordering Cultures:

If you have a certain virus in mind, specifically order the type of virus culture you are interested in (e.g. CMV, HSV, enterovirus). If you just order "viral screen", CMV for instance is not included. The screen includes numerous cultures on several different cell culture media and therefore the sample sent is often not sufficient for all of these. This reduces the yield for the one virus you want to test for and it is also a lot more expensive than a single cell culture.

The contact names and numbers for the Virology Lab:

Virology: Director Peter Wright, MD. Lab supervisor (and person to call to ask for sample processing is Wray Estes at 343-9162
 

PCR: Molecular Infectious Diseases (ID) Laboratory of Dr. Yi-Wei Tang, Assistant Professor of Medicine and Pathology at 343-1289. He is very helpful and eager to try new things, also very willing to collaborate in research projects. He would be the one to discuss exactly what to send for what and where and how. After discussion with him, he is often willing to run samples stat or type of samples (with a disclaimer) that usually are not approved or available at WizOrder. But if the golden standard is not available, this can be very helpful for diagnosis.

While you are waiting for lab results, you can do imaging of brain and abdominal organs and get an ophthalmology exam for chorioretinitis. In particular the eye exam is very helpful and is often forgotten.