AMERICAN JOURNAL OF PERINATOLOGY/VOLUME 9, NUMBER 4
July 1992
TRANSPLACENTAL IMMUNITY TO VARICELLA-ZOSTER VIRUS IN EXTREMELY LOW BIRTHWEIGHT INFANTS David B. Mendez, M.D., Mary Beth Sinclair, B.S., Sylvia Garcia, R.N., Theresa Chou, R.N., and William Meadow, M.D., Ph.D.
Sixteen infants in our intensive care nursery (ICN) were inadvertently exposed to an adult who presented the next day with chickenpox. Since a majority of the patients were extremely premature, we were concerned that they might not have received transplacental varicella-zoster virus (VZV) antibody, and consequently would be at risk for contracting chickenpox. Serum samples were obtained from each infant and examined for the presence or absence of VZV antibody. Fourteen of the 16 infants had antibody levels equal to or in excess of 1:16 by indirect fluorescent antibody, including six of eight infants with birthweights equal to or less than 1000 gm, and eight of ten infants with gestational ages equal to or less than 28 weeks. Passive transfer of immunity to VZV appears to be common in infants as young as 24 to 28 weeks' gestation.
Increased survival of extremely premature infants has raised more frequent concerns regarding their immunocompetence and susceptibility to a variety of infectious agents. Varicella-zoster virus (VZV) is one such agent. Effective transplacental transfer of VZV antibody for term infants was demonstrated in the mid-1960s.1 It has been suggested that transfer of immunoglobulin across the placenta occurs primarily during the third trimester2 and that antibody titers are related to the overall weight of the neonate.3 Consequently, low birthweight infants may not have received the full complement of transplacental antibody at the time of their birth. Sixteen infants in our intensive care nursery were inadvertently exposed to an adult man who presented the next day with the clinical stigma of chickenpox. In an attempt to determine which, if any, of our patients might require prophylactic therapy with varicella-zoster immune globulin (VZIG), we determined the VZV antibody status of each of the 16 infants.
contains VZV antibody) when more than 15% of the infected human fibroblast cells in each field exhibit a greenish-yellowfluorescence.The remaining infected cells not bound by antibody provide a contrasting red background. A positive reaction at a dilution of 1:16 or greater was taken to indicate the presence of antibody to VZV and immunity to VZV.4 The reference VZV IFA kit was from Electro-Nucleonics, Inc (ENI). In a total of 124 samples, there was 100% agreement, 100% sensitivity, and 100% specificity between the Gull VZV test and the reference test kit. Specific performance characteristics of the reference test kit from ENI were compared in a blind study with a fluorescent antimembrane antigen (FAMA), used at a research center for evaluation of VZV immune status. The data generated in the blind study show the ENI VZV IFA test to be nearly three-fold more sensitive than the reference FAMA. Plotting only those samples positive at 1:8 or greater by both methods (146 samples) the geometric mean titer was found to be 270 for the ENI IFA test and 97 for the FAMA.4
MATERIALS AND METHODS Serum samples were obtained from each of the patients either by heel stick or arterial puncture. Detection of VZV antibody was performed by using the indirect fluorescent antibody (IFA) technique (Gull Laboratories, Salt Lake City, UT). The serum is considered positive (that is,
RESULTS
The clinical characteristics and VZV status of each patient are described in Table 1. Fourteen of the 16 (87.5%) infants were noted to have detectable VZV anti-
Department of Pediatrics, Wyler Children's Hospital, The University of Chicago, Chicago, Illinois Reprint requests: Dr. Mendez, Department of Pediatrics, Wyler Children's Hospital, University of Chicago, Chicago, IL 60637 236
Copyright © 1992 by Thieme Medical Publishers, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.
Downloaded by: National University of Singapore. Copyrighted material.
ABSTRACT
VARICELLA-ZOSTER VIRUS IMMUNITY/Mendez, et al. Table 1. Clinical Characeristics and Varicella-Zoster Titer Results in 16 Infants Gender
Birthweight (gm)
Gestational Age (weeks)
Age at Test (days)
AG CS
F F
540 594
23 24
90 26
CH SH
LJ_ U_
710 780
28 28
55 55
EY AL
F M M
790 930 1000
24 28 27
62 38 9
1000 1100 1110 1389 1460 1630 1840 2460 2515
28 28 27 30 32 32 35 35 36
24 51 27 20 7 6 4 4 4
P] ES RB
M M M M
RM
u_
BG AM GG DS DS BM
M M M M
Titer Results*
Prior Blood Products Washed packed red Washed packed red plasma Washed packed red Washed packed red frozen plasma Washed packed red Washed packed red Washed packed red plasma Washed packed red Washed packed red Washed packed red Washed packed red Washed packed red
blood cells, 5% albumin blood cells, fresh frozen blood cells blood cells, platelets, fresh blood cells blood cells blood cells, fresh frozen
blood blood blood blood blood
cells cells cells cells cells Downloaded by: National University of Singapore. Copyrighted material.
Case
Washed packed red blood cells
*Titer considered positive if dilution was equal to or greater than 1:16.
body at a titer greater than or equal to 1:16. Subsets of these 16 infants included eight of ten (80%) infants with gestational age less than or equal to 28 weeks, six of eight (75%) infants with birthweight less than or equal to 1000 gm, and four of five (80%) infants with birthweight equal to or less than 800 gm. Thirteen of the 16 patients, including both infants who were VZV antibody negative, had received blood products (primarily washed packed red blood cells) prior to the determination of their VZV antibody status. The VZV antibody status of the mothers of the two seronegative children was not known to us, nor were we granted permission to test these mothers for the presence of VZV antibody. The two infants whose VZV antibody titer was negative received VZIG 0.5 cc/kg intramuscularly in a one-time dose5 given to the infants within 48 hours of exposure. None of the 16 children developed any symptoms suggestive of VZV infection in the subsequent 28 days of observance after exposure to VZV.
DISCUSSION The number of newborn babies who are at risk for VZV infection in the nursery is believed to be related to the overall seropositivity of parturient mothers,6 the intensity of the exposure to the virus,7-8 and the level of antibody placentally transferred by the mother to her infant. 1>3-9 Since the neonate is dependent on passive transfer of anti-
body for the acquisition of immunity to VZV during gestation, birthweight and gestational age are believed to play a role in determining the timing and amount of antibody received.23-58 For premature infants, the question arises as to when neonates are "too young" or "too small" to have received adequate transplacental immunoprotection. These babies, as well as those born to seronegative mothers, should be the focus of therapeutic intervention with VZIG. We have demonstrated that 14 of 16 intensive care nursery patients ranging in age from 4 to 90 days were seropositive for VZV antibody, including eight of ten (80%) infants with gestational age less than or equal to 28 weeks, six of eight (75%) with birthweight less than or equal to 1000 gm, and four of five (80%) with birth weights less than 800 gm. Previous published reports of VZV antibody titers in premature infants are summarized in Table 2. The eight infants in our series with birthweight less than 1000 grams comprise 8 of 13, or 62% of all reported cases in infants of this birthweight. The five patients with birthweight less than 800 gm comprise five of six, or 83%, of all such reported cases at this birthweight.39 Thirteen of our 16 patients had received blood products, including washed packed red blood cells (n = 13), fresh frozen plasma (n = 3), and 5% albumin (n = 1). The possibility arises that our patients received antibody to VZV through these products. Three lines of evidence suggest that this is unlikely: (1) all packed red blood cells were washed with saline, a procedure designed to remove transfusion of plasma products; (2) Wang et al3 reported no
Table 2. Tabulation of Infants from Studies That Listed Titer Presence or Absence in Relationship to Gestational Age and Birthweight Reference Wang et al Raker et al Mendez et al (this study)
Gestational Age (
July 1992
TRANSPLACENTAL IMMUNITY TO VARICELLA-ZOSTER VIRUS IN EXTREMELY LOW BIRTHWEIGHT INFANTS David B. Mendez, M.D., Mary Beth Sinclair, B.S., Sylvia Garcia, R.N., Theresa Chou, R.N., and William Meadow, M.D., Ph.D.
Sixteen infants in our intensive care nursery (ICN) were inadvertently exposed to an adult who presented the next day with chickenpox. Since a majority of the patients were extremely premature, we were concerned that they might not have received transplacental varicella-zoster virus (VZV) antibody, and consequently would be at risk for contracting chickenpox. Serum samples were obtained from each infant and examined for the presence or absence of VZV antibody. Fourteen of the 16 infants had antibody levels equal to or in excess of 1:16 by indirect fluorescent antibody, including six of eight infants with birthweights equal to or less than 1000 gm, and eight of ten infants with gestational ages equal to or less than 28 weeks. Passive transfer of immunity to VZV appears to be common in infants as young as 24 to 28 weeks' gestation.
Increased survival of extremely premature infants has raised more frequent concerns regarding their immunocompetence and susceptibility to a variety of infectious agents. Varicella-zoster virus (VZV) is one such agent. Effective transplacental transfer of VZV antibody for term infants was demonstrated in the mid-1960s.1 It has been suggested that transfer of immunoglobulin across the placenta occurs primarily during the third trimester2 and that antibody titers are related to the overall weight of the neonate.3 Consequently, low birthweight infants may not have received the full complement of transplacental antibody at the time of their birth. Sixteen infants in our intensive care nursery were inadvertently exposed to an adult man who presented the next day with the clinical stigma of chickenpox. In an attempt to determine which, if any, of our patients might require prophylactic therapy with varicella-zoster immune globulin (VZIG), we determined the VZV antibody status of each of the 16 infants.
contains VZV antibody) when more than 15% of the infected human fibroblast cells in each field exhibit a greenish-yellowfluorescence.The remaining infected cells not bound by antibody provide a contrasting red background. A positive reaction at a dilution of 1:16 or greater was taken to indicate the presence of antibody to VZV and immunity to VZV.4 The reference VZV IFA kit was from Electro-Nucleonics, Inc (ENI). In a total of 124 samples, there was 100% agreement, 100% sensitivity, and 100% specificity between the Gull VZV test and the reference test kit. Specific performance characteristics of the reference test kit from ENI were compared in a blind study with a fluorescent antimembrane antigen (FAMA), used at a research center for evaluation of VZV immune status. The data generated in the blind study show the ENI VZV IFA test to be nearly three-fold more sensitive than the reference FAMA. Plotting only those samples positive at 1:8 or greater by both methods (146 samples) the geometric mean titer was found to be 270 for the ENI IFA test and 97 for the FAMA.4
MATERIALS AND METHODS Serum samples were obtained from each of the patients either by heel stick or arterial puncture. Detection of VZV antibody was performed by using the indirect fluorescent antibody (IFA) technique (Gull Laboratories, Salt Lake City, UT). The serum is considered positive (that is,
RESULTS
The clinical characteristics and VZV status of each patient are described in Table 1. Fourteen of the 16 (87.5%) infants were noted to have detectable VZV anti-
Department of Pediatrics, Wyler Children's Hospital, The University of Chicago, Chicago, Illinois Reprint requests: Dr. Mendez, Department of Pediatrics, Wyler Children's Hospital, University of Chicago, Chicago, IL 60637 236
Copyright © 1992 by Thieme Medical Publishers, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.
Downloaded by: National University of Singapore. Copyrighted material.
ABSTRACT
VARICELLA-ZOSTER VIRUS IMMUNITY/Mendez, et al. Table 1. Clinical Characeristics and Varicella-Zoster Titer Results in 16 Infants Gender
Birthweight (gm)
Gestational Age (weeks)
Age at Test (days)
AG CS
F F
540 594
23 24
90 26
CH SH
LJ_ U_
710 780
28 28
55 55
EY AL
F M M
790 930 1000
24 28 27
62 38 9
1000 1100 1110 1389 1460 1630 1840 2460 2515
28 28 27 30 32 32 35 35 36
24 51 27 20 7 6 4 4 4
P] ES RB
M M M M
RM
u_
BG AM GG DS DS BM
M M M M
Titer Results*
Prior Blood Products Washed packed red Washed packed red plasma Washed packed red Washed packed red frozen plasma Washed packed red Washed packed red Washed packed red plasma Washed packed red Washed packed red Washed packed red Washed packed red Washed packed red
blood cells, 5% albumin blood cells, fresh frozen blood cells blood cells, platelets, fresh blood cells blood cells blood cells, fresh frozen
blood blood blood blood blood
cells cells cells cells cells Downloaded by: National University of Singapore. Copyrighted material.
Case
Washed packed red blood cells
*Titer considered positive if dilution was equal to or greater than 1:16.
body at a titer greater than or equal to 1:16. Subsets of these 16 infants included eight of ten (80%) infants with gestational age less than or equal to 28 weeks, six of eight (75%) infants with birthweight less than or equal to 1000 gm, and four of five (80%) infants with birthweight equal to or less than 800 gm. Thirteen of the 16 patients, including both infants who were VZV antibody negative, had received blood products (primarily washed packed red blood cells) prior to the determination of their VZV antibody status. The VZV antibody status of the mothers of the two seronegative children was not known to us, nor were we granted permission to test these mothers for the presence of VZV antibody. The two infants whose VZV antibody titer was negative received VZIG 0.5 cc/kg intramuscularly in a one-time dose5 given to the infants within 48 hours of exposure. None of the 16 children developed any symptoms suggestive of VZV infection in the subsequent 28 days of observance after exposure to VZV.
DISCUSSION The number of newborn babies who are at risk for VZV infection in the nursery is believed to be related to the overall seropositivity of parturient mothers,6 the intensity of the exposure to the virus,7-8 and the level of antibody placentally transferred by the mother to her infant. 1>3-9 Since the neonate is dependent on passive transfer of anti-
body for the acquisition of immunity to VZV during gestation, birthweight and gestational age are believed to play a role in determining the timing and amount of antibody received.23-58 For premature infants, the question arises as to when neonates are "too young" or "too small" to have received adequate transplacental immunoprotection. These babies, as well as those born to seronegative mothers, should be the focus of therapeutic intervention with VZIG. We have demonstrated that 14 of 16 intensive care nursery patients ranging in age from 4 to 90 days were seropositive for VZV antibody, including eight of ten (80%) infants with gestational age less than or equal to 28 weeks, six of eight (75%) with birthweight less than or equal to 1000 gm, and four of five (80%) with birth weights less than 800 gm. Previous published reports of VZV antibody titers in premature infants are summarized in Table 2. The eight infants in our series with birthweight less than 1000 grams comprise 8 of 13, or 62% of all reported cases in infants of this birthweight. The five patients with birthweight less than 800 gm comprise five of six, or 83%, of all such reported cases at this birthweight.39 Thirteen of our 16 patients had received blood products, including washed packed red blood cells (n = 13), fresh frozen plasma (n = 3), and 5% albumin (n = 1). The possibility arises that our patients received antibody to VZV through these products. Three lines of evidence suggest that this is unlikely: (1) all packed red blood cells were washed with saline, a procedure designed to remove transfusion of plasma products; (2) Wang et al3 reported no
Table 2. Tabulation of Infants from Studies That Listed Titer Presence or Absence in Relationship to Gestational Age and Birthweight Reference Wang et al Raker et al Mendez et al (this study)
Gestational Age (
