Comparison of two methods for detecting varicella-zoster virus antibody with varicella-zoster virus cell-mediated immunity.

We evaluated an enzyme-linked immunoassay (EIA; BioWhittaker) and a latex agglutination (LA; Becton Dickinson) for varicella-zoster virus (VZV) antibody determination, using cell-mediated immunity (CMI) as a "gold standard." VZV EIA had a sensitivity, specificity, positive predictive value, and negative predictive value of 87, 91, 87, and 91%, respectively, compared with CMI. Correlation was excellent except when the varicella index was 0.9 to 1.2. We defined sera with varicella indices of 0.9 to 1.2 as indeterminate. LA had a sensitivity, specificity, positive predictive value, and negative predictive value of 96, 91, 97, and 90%, respectively, compared with EIA. LA reactivity only at a 1:2 dilution did not correlate with CMI, but sera reactive at dilutions of > or = 1:8 indirectly did. We defined indeterminate sera as those reactive at 1:2 and nonreactive at 1:8. EIA and LA were equivalent for determining VZV immune status, and both methods required modified criteria of interpretation to increase their specificity.

In vitro activities of penciclovir and acyclovir against herpes simplex virus types 1 and 2.

Penciclovir (PCV) and acyclovir are acyclic guanine analogs which inhibit herpes simplex virus (HSV) DNA polymerase. Their 50% infective doses were 0.5 to 0.8 microgram/ml for clinical isolates of HSV-1 and 1.3 to 2.2 micrograms/ml for HSV-2. Furthermore, HSV-infected cultures receiving 2-h pulses of PCV had 2- to 50-fold less HSV than acyclovir-treated cultures, consistent with the prolonged intracellular half-life of PCV triphosphate.

Detection of respiratory syncytial virus antigen in nasal washings by Abbott TestPack enzyme immunoassay.

We compared the new Abbott TestPack (TP) respiratory syncytial virus (RSV) enzyme immunoassay (EIA) with cell culture and two commercial RSV EIAs (from Abbott Diagnostics and Kallestad Laboratories) by using split samples of fresh nasal washings from children with suspected RSV disease. Two tubes of HEp-2 cells were inoculated and observed for cytopathic effect for 14 days, and isolates were confirmed by immunofluorescence. The TP EIA was performed by following the manufacturer's instructions. Specimens positive by TP EIA but negative by culture were examined in a competitive inhibition (blocking) assay using the TP EIA, and rabbit anti-RSV serum. Of 218 specimens, 93 were positive by culture, 105 were positive by TP EIA, 80 were positive by the Abbott Diagnostics EIA, and 87 were positive by the Kallestad Laboratories EIA. The sensitivity, specificity, positive predictive value, and negative predictive value of the TP EIA were 92, 86, 81, and 93%, respectively. Of 20 apparently false-positive TP EIAs, 10 of 14 that were positive when retested were neutralized in the blocking assay, indicating that they were truly positive. The recalculated sensitivity, specificity, positive predictive value, and negative predictive value of the TP EIA were 92, 91, 90, and 93%, respectively. We conclude that the TP EIA is easy to perform, rapid (less than 0.5 h), and accurate.

Detection of respiratory syncytial virus antigen in nasopharyngeal secretions by Abbott Diagnostics enzyme immunoassay.

We compared a rapid respiratory syncytial virus (RSV) antigen enzyme immunoassay (EIA) (Abbott Diagnostics, North Chicago, Ill.) with virus culture and with the indirect fluorescent-antibody test (FAT) by using nasopharyngeal washings from children with suspected RSV pneumonia or bronchiolitis. Fresh washings were used in all three tests. Specimens were inoculated into HEp-2 cells and human embryonic lung fibroblasts and observed for cytopathic effect. Cells in the centrifuged sediments of the nasal washes were examined for typical cytoplasmic fluorescence of RSV by FAT. The EIA cutoff was an optical density (OD) at 492 nm that was greater than the mean OD of the negative controls plus 0.1. An OD within +20% of the cutoff was considered borderline, and these specimens were retested. Of 289 specimens, 118 (41%) were positive by culture, 150 (52%) were positive by FAT, and 154 (53%) were positive by EIA. Eight borderline EIAs were all negative when the specimens were retested after storage at -70 degrees C. Of 17 specimens positive by EIA but negative by culture and FAT, 9 were blocked in a competitive EIA, indicating that they were true-positives and that the culture and FAT were falsely negative. The sensitivity, specificity, and predictive value (positive) of the EIA versus culture, FAT, or blocking assay were 90, 94, and 95%, respectively. We conclude that the Abbott RSV antigen EIA is highly sensitive and specific.

Toxic effect of calcium alginate swabs on Neisseria gonorrhoeae.

Calcium alginate (CA)-tipped swabs have been reported to interfere with the recovery of herpes simplex virus, Chlamydia trachomatis, and Ureaplasma urealyticum and may cause cytotoxicity in cell culture. To determine whether CA swabs also inhibit the growth of Neisseria gonorrhoeae, we carried out a series of experiments using either CA swabs that were toxic or nontoxic in a cell culture cytotoxicity assay or nontoxic rayon or cotton swabs. Leaving a toxic CA swab in 3 ml of Mueller-Hinton broth inoculated with 10(4) CFU/ml caused rapid killing within 6 h at 37 degrees C; colony counts of five strains were less than 1% of those of Mueller-Hinton broth controls. When the tips of toxic CA swabs were inoculated directly and kept at 37 degrees C without holding medium, the swabs were sterile at 6 h. If the same swabs were placed in Amies medium with charcoal, organisms could still be recovered at 6 h. Toxicity was less at room temperature than at 37 degrees C. Inhibition of growth of N. gonorrhoeae was not seen with rayon or cotton swabs. The toxic component was neither the CA fiber nor the aluminum wire but probably the glue used to attach the fibers. We concluded that some lots of CA swabs kill N. gonorrhoeae in vitro. Survival of N. gonorrhoeae is improved with nontoxic swabs, particularly cotton swabs, and Amies medium with charcoal regardless of swab type.

Comparison of nasopharyngeal washings and swab specimens for diagnosis of respiratory syncytial virus by EIA, FAT, and cell culture.

Respiratory secretions for viral diagnosis are often collected with nasopharyngeal (NP) swabs, although many laboratories recommend NP aspirates or washings. We compared results using NP washings and NP swabs in three diagnostic RSV tests, a rapid RSV EIA antigen test (Abbott Laboratories), an indirect fluorescent antibody test (FAT) with rabbit antiserum, and virus culture (HEp-2 cells). Paired samples were collected from 121 children with suspected RSV bronchiolitis or pneumonia. A minitip swap was passed into the nasopharynx for 10 sec, rotated and withdrawn. The opposite nares was irrigated with approximately 1 ml of saline and aspirated using a syringe and plastic feeding tube. Fifty-one children (42%) grew RSV in culture, 49 from NP washings versus 27 from NP swabs (p less than 0.001). Fifty-three (44%) were positive by FAT, 52 from NP washings versus 12 from NP swabs (p less than 0.001). Fifty-eight children (48%) had positive RSV EIA tests, 57 from NP washings versus 35 from NP swabs (p less than 0.001). Detection by EIA was more sensitive than culture regardless of the method of specimen collection. We conclude that NP washings are superior to NP swabs for RSV culture and rapid diagnosis by EIA or FAT.

The immunologic response to infection with respiratory syncytial virus in infants.

Fifty infants younger than six months, hospitalized for infection with respiratory syncytial virus (RSV), were studied by examination of serial samples of nasal secretion. Secretory neutralizing activity was measured by plaque reduction and secretory antibody by indirect fluorescence using conjugated antiserum to human IgA, IgG, or IgM. Secretory neutralizing activity during infection rose or fell fourfold with approximately equal frequency (20% and 26%, respectively). In contrast, levels of IgA antibody to RSV in secretions rose fourfold in 56%--65% of the infants and fell in none. The frequency of such rises in titer of antibody was directly related to age. In individual secretions the correlation between neutralizing activity and IgA antibody to RSV was poor: neutralizing activity was often found in the absence of detectable antibody, and IgA antibody to RSV was often nonneutralizing. Nevertheless, the development of IgA antibody to RSV correlated in time with the disappearance of virus from the respiratory tract. The timing of this secretory response is consistent with the hypothesis that antibody contributes significantly to cure of infection.