br Study design br Results To explore
Results To explore potential differences in the volume the different swabs absorb, the loss of weight of tubes filled with water after soaking the different swabs under defined conditions was determined. This revealed that the different swabs absorbed between approximately 0.07 and 0.1 ml (Table 2). Based on the absorbed volume and the CMV DNA concentration of two Memantine hydrochloride suspensions, the hypothetical viral load of each swab was calculated. In the absence of a joint standard, viral load determinations may differ several-fold between laboratories. Since we aimed to compare recovery efficiencies for the different swabs between two different laboratories, the CMV DNA concentrations of aliquots of the same two virus suspensions were determined independently in both laboratories. This revealed 3-fold lower CMV DNA concentrations for both virus suspensions in laboratory 2. Therefore, different hypothetical viral loads were calculated for each laboratory. The impact of the different swab types and the duration of storage on the recovery efficiency of CMV DNA was determined for virus suspension 1 (Fig. 1a) and 2 (Fig. 1b). Comparing the CMV DNA concentration determined for each of the experimental conditions to the hypothetical values provided a measure of efficiency of recovery that also allowed comparison between the two laboratories. Recovered virus concentrations of the particular swab types were similar at different time points as illustrated by Fig. 1. Thus, CMV DNA recovery of the different swabbing materials seems to be independent of the duration of storage reflecting the transport time. However, the swab and transport medium seemed to affect recovery efficiency to a larger extent. Swab no. 1 revealed a significantly lower recovery than the same swab used with VTM (swab no. 3) at each time point (Fig. 1a, b). In contrast, there is obviously no such difference between the second dry swab (swab no. 2) and the same swab soaked with VTM (swab no. 4). The reproducibility within the same swabs was predominantly excellent. To quantitatively assess potential differences in CMV DNA recovery between different sampling procedures, the mean CMV DNA recovery for both virus suspensions at all time points in both laboratories was calculated for each swab type (Fig. 2). Swabs no. 3 and 6 showed the highest mean recovery of CMV DNA. Statistical analysis of CMV DNA recovery rates of the swabs analysed (no. 1-6) using one-way ANOVA showed significant differences (p < 0.0001). Results of the group to group comparisons with the Tukey´s Multiple Comparison Test are shown in Fig. 2. With swab no. 1 the lowest recovery rate of all swab types could be detected (40% of hypothetical value, Fig. 2) – this amount is significantly lower than in three other swab types (Fig. 2). Furthermore, flocked swab with eNat medium (swab no. 6) had the highest mean recovery rate (160% of hypothetical value, Fig. 2) that differed significantly from the recovery rates from swab 1, 4 and 5 (Fig. 2).
Discussion Congenital CMV infection is the most common non-genetic cause of SNHL in childhood. The fact that most congenitally infected infants are asymptomatic at birth underlines the need for postnatal CMV screening, as early detection is essential for directed care . The ideal screening method should be rapid, sensitive, cost effective and amenable to high-throughput testing. Saliva is easy to collect with swabs and PCR methods are widely used. Reports in the past indicate that this approach has good analytical performance and clinical sensitivity and may be able to fulfill the criteria for qualitative screening purposes . Nevertheless the rate of false positive quantitative real time (qrt) PCR results from saliva compared to confirmation with PCR from urine was reported discordantly ranging from 1.2%  to 16% . Importantly, contamination of saliva with CMV after breastfeeding leading to false positive PCR results seems to be less critical than previously thought .