New screening tests: HSV, CMV, HBV, HCV, parvovirus, and HIV
Tips on choosing the right tests and getting valid results
Referral for GI consultation is indicated for Jessica’s management. The finding of HCV virus also influences which contraceptives she should be offered: Avoid any hormonal contraceptive metabolized by the liver.
Parvovirus B19
GRETCHEN’S CASE
Pregnant and occupationally exposed
Gretchen is a 31-year-old elementary school teacher who is 20 weeks pregnant with her second child. She schedules an appointment with you because she is concerned about cases of B19, or Fifth disease, reported at her school. She has been teaching in the school for 7 years and has never been tested for B19 infection. She reports no symptoms and observes that there have been no cases of B19 among the students in her classroom.
You order IgG antibody testing, which reveals that Gretchen has immunity.
In light of this finding, how do you counsel her?
Gretchen can be reassured that, though she was obviously infected in the past, B19 poses no risk to this pregnancy. Roughly 50% of women are, like Gretchen, already immune to B19. Even if a woman is exposed to the virus during pregnancy, both she and the fetus are usually only mildly affected. However, B19 infection can cause severe anemia in the fetus and trigger spontaneous abortion—although this occurs in less than 5% of pregnancies infected with B19 and is more likely to occur during the first half of a pregnancy. Fetal exposure to B19 appears to cause no birth defects or mental retardation.
In general, testing for B19 in pregnancy is warranted after exposure to the virus to assess immunity or susceptibility. The best way to do so is by testing for IgM and IgG antibodies using an ELISA technique. The IgM antibody is produced within a few days of primary infection and persists for 2 to 3 months. The IgG antibody can be found 1 week after acute infection and persists perhaps for life.
The finding of the IgG antibody in an immunocompetent patient with no IgM antibody demonstrates immunity.13,14 In some cases, additional testing using an IgG avidity assay and/or B19 DNA PCR may be necessary.15
TABLE
Sensitivity and specificity of viral screening tests
| TESTS | SENSITIVITY (%) | SPECIFICITY (%) | COMMENT |
|---|---|---|---|
| Genital herpes | |||
| IgG (ELISA) | Must be type-specific based on gG protein | ||
| HSV-1 | 91–96 | 96–97 | |
| HSV-2 | 96–100 | 92–95 | |
| Point-of-care rapid test (biokitHSV-2) | 99–100 | 96–97 | Only for HSV-2 |
| IgM | DO NOT USE | ||
| Culture of lesion in mother | 50 | 90 | Positive result clinically useful |
| PCR | >90 | >90 | Usually reserved for testing cerebrospinal fluid for encephalitis (in newborns, children, and adults) |
| Cytomegalovirus | |||
| IgG | >90 | 80–92 | |
| IgM | 65–78 | 65–82 | |
| Culture of amniotic fluid | 70 (newborns with CMV) | 100 | Culture of the amniotic fluid may be negative even with infection |
| PCR of amniotic fluid | 77 | 100 | |
| Hepatitis B | |||
| HBcAb | 95 | 95 | Marker of past infection |
| HBsAb | 95 | 95 | Only marker post-vaccination |
| HBsAg | 95 | 95 | Carrier |
| HBeAb | Marker of past infection | ||
| HBeAg | Only in carrier state. Carrier who also demonstrates HBeAg has a high risk of transmission to the newborn | ||
| Hepatitis C | |||
| HCVAb (ELISA) | 99 | 99 | 3rd-generation ELISA |
| HCV RNA-PCR | >95 | >95 | Correlates with infectivity |
| Parvovirus B19 | |||
| IgG (ELISA) | 97 | 94 | |
| IgM (antibody capture enzyme immunoassay) | 89 | 99 | Must use a reliable lab for determination of IgM because of the high incidence of false positives |
| PCR in fetus | 92 | 94 | Currently, reference lab can perform this test. Use on amniotic fluid to confirm in utero infection after primary infection in the mother is diagnosed |
| Human immunodeficiency virus | |||
| ELISA | 99 | 99 | Screening test, repeated if positive |
| Western blot | 99 | 99 | Confirmatory test |
| p24 antigen | May be positive early in acute infection before antibody response | ||
| HIV-1 RNA by PCR | May be positive early in acute infection before antibody response | ||
| ELISA=Enzyme-linked immunosorbent assay; HBcAb=hepatitis B core antibody; HBeAb=hepatitis B early antibody; HBeAg=hepatitis B early antigen; HBsAb=hepatitis B surface antibody; HBsAg=hepatitis B surface antigen; HCV=hepatitis C virus; HSV=herpes simplex virus; Ig=immunoglobulin; PCR=polymerase chain reaction. | |||
ANGELA’S CASE
Recurrent vaginitis and numerous sexual partners
After 2 years of recurrent yeast infections, 41-year-old Angela comes to your office seeking more definitive therapy. She says she is tired of frequent infections that respond to oral and topical therapy but recur less than a week after therapy ends. She reports that she was divorced 8 years ago and has had numerous sexual partners since then. One in particular had a history of drug abuse. In response to your questions, Angela reports no history of diabetes or drug abuse herself.
Physical examination reveals severe external vulvar erythema and edema, and severe vaginal overgrowth of a “cottage-cheese” discharge consistent with Candida vaginitis. Given Angela’s history and physical findings, you order an HIV test, obtaining written permission for it. The test is reported as positive.
Does Angela have HIV?
It is impossible to tell without a repeat ELISA test and confirmation by Western blot, because false-positive results do occur.
Testing for HIV is now common in ObGyn offices. All women who are sexually active, diagnosed with another STD, or are pregnant are encouraged to undergo HIV screening. Testing may need to be repeated within 6 months in consideration of the incubation period of the virus. If the woman has a new relationship or additional history of high-risk sexual practices, testing should also be repeated.
