Acute gastroenteritis is one of the most common diseases worldwide. In developed countries, viruses, particularly noroviruses, are recognized as the leading cause. In The Netherlands, the surveillance of gastroenteritis outbreaks with suspected viral etiologies (as determined by Kaplan criteria) was established by the National Institute for Public Health and the Environment in 1994. This paper presents an overview of viral gastroenteritis outbreaks reported from 1994 through 2005. A minimum epidemiological data set consisting of the associated setting(s), the probable transmission mode, the date of the first illness and the date of sampling, the number of persons affected, and the number of hospitalizations was requested for each reported outbreak. Stool samples were tested for the presence of norovirus, sapovirus, rotavirus, astrovirus, adenovirus, and Aichi virus by electron microscopy, enzyme-linked immunosorbent assay, and/or reverse transcription-PCR. A total of 6,707 stool samples from 941 gastroenteritis outbreaks were investigated. Noroviruses were detected as the causative agent in 735 (78.1%) of the outbreaks, and rotaviruses, adenoviruses, and astroviruses were found to be responsible for 46 (4.9%), 9 (1.0%), and 5 (0.5%) outbreaks, respectively. Among the gastroenteritis outbreaks in which a mode of transmission was identified, most outbreaks (38.1%) were associated with person-to-person transmission, and the majority (54.9%) of the outbreaks investigated were reported by residential institutions. Since 2002, the total number of outbreaks reported and the number of unexplained outbreaks have increased. Furthermore, the number of rotavirus-associated outbreaks has increased, especially in nursing homes. Despite thorough testing, 115 (12.2%) outbreaks suspected of having viral etiologies remain unexplained. Increases in numbers of reported outbreaks may indicate undefined changes in the criteria for reporting or the emergence of new pathogens.

Sapoviruses (SaVs) belong to the Caliciviridae family and can cause gastroenteritis in humans and swine. Despite extensive testing, human sapoviruses have been found only in sporadic cases and in one mixed outbreak in children between 1994 and 2007 in the Netherlands. Here we describe a change in sapovirus epidemiology in the Netherlands resulting in sapovirus outbreaks and infections in adults. From November 2007 to January 2009, 478 outbreaks of acute gastroenteritis were reported to the National Institute for Public Health and the Environment in the Netherlands as a part of ongoing surveillance. Sapoviruses were found to be the most likely cause of 19 outbreaks (4%). During the same 2-year period, sapovirus infections were reported in Sweden, Slovenia, and Hungary. In the Netherlands, further characterization of outbreak strains showed that 12 (63%) sapovirus outbreaks were caused by genotype I.2 viruses. Most patients were adults older than 60 years (range, 1 to 100 years). Phylogenetic analysis using all presently available SaV sequences showed high homology between genotype I.2 strains detected in different geographical regions (Sweden, Slovenia, Taiwan, Japan, and Russia) since 2007. These first reported outbreaks of sapovirus infections in adults in the Netherlands were remarkable. Detection of identical genotypes in many samples might suggest that these viruses have the same origin, and since the infection is spreading fast, the prevalence of sapovirus infection may be increasing. The incidence of sapovirus infections in these countries suggests that a substantial part of Europe is affected by this virus.

Coxiella burnetii is the causative agent of Q fever. The bacterium is highly infectious and is classified as a category B biological weapon. The tools of molecular biology are of utmost importance in a rapid and unambiguous identification of C. burnetii in naturally occurring Q fever outbreaks, or in cases of a deliberate release of the infectious agent. In this work, development of a multiple locus variable number tandem repeats (VNTR) analysis (MLVA) for the characterization of C. burnetii is described. Sixteen C. burnetii isolates and five passage history/laboratory variants were characterized. The VNTR markers revealed many polymorphisms resulting in nine unique MLVA types that cluster into five different clusters. This proves that the MLVA system is highly discriminatory. The selected VNTR markers were stable. The MLVA method developed in this report is a promising tool for the characterization of C. burnetii isolates and their epidemiological study.

Acute gastroenteritis is one of the most common diseases worldwide, with viruses, particularly noroviruses, being the leading cause in developed countries. In The Netherlands, systematic surveillance of gastroenteritis outbreaks of suspected viral etiology was established by the National Institute for Public Health and the Environment in 1994. Since 2002, the total number of outbreaks reported has been increasing, and with that comes the need for sensitive assays that can be performed quickly. In addition, the diagnostic demand changed so that now the proportion of samples from hospitals is higher and there is a need for patient-based test results. In order to target the diagnosis of acute gastroenteritis, we reviewed our data on outbreaks of gastroenteritis and the prevalence of individual viruses to provide a priority list of viruses for which samples should be evaluated. Random primers were used to replace the separate specific primers for each virus used in the reverse transcription steps. The individual PCR assays were replaced by multiplex PCR assays. We employed a two-step method in which in the first step we screened for the most common causes of viral gastroenteritis, noroviruses of genogroup II and rotaviruses of group A, with equine arteritis virus used as the internal control. Subsequently, in the second step, two parallel PCR assays were developed for the detection of noroviruses of genogroup I and equine arteritis virus in one run and adenoviruses, sapoviruses, and astroviruses in the other run. The specificities of the assays were calculated to be 92.5% for the assay for noroviruses of genogroup I and 100% for the assays for all other viruses, the detection limits were equal for all viruses, and the turnaround time was reduced to 1 day compared to the at least 3 days required for the methods used previously. This approach allows the targeted, rapid, and cost-effective elucidation of the causes of acute gastroenteritis outbreaks.

The use of metagenomics for virus discovery in clinical samples has opened new opportunities for understanding the aetiology of unexplained illness. This study explores the potential of this sequence-independent approach in a public-health setting, by systematic analysis of samples cultured from patients with unexplained illness through a combination of PCR-based assays and viral metagenomics. In total, 1834 cell-culture isolates were collected between 1994 and 2007 through the Enterovirus Surveillance programme in the Netherlands. During the 13 year period, seven samples that exhibited reproducible cytopathogenic effects in cell culture tested negative in standard PCR assays for a range of viruses. In order to fill the diagnostic gap, viral metagenomics was applied to these culture supernatants, resulting in the rapid identification of viruses in all of the samples. The unexplained samples contained BK polyomavirus, herpes simplex virus, Newcastle disease virus and the recently discovered Saffold viruses (SAFV) (which dominated the unexplained samples; n54). The full genomic sequences of four SAFV genotype 3 (SAFV-3) viruses, which share 88-93 % nucleotide identity with known SAFV-3 viruses, are reported. Further screening for SAFV in additional cultured, unidentified clinical isolates from 2008 and 2009 resulted in identification of another SAFV-positive sample. Although the pathogenicity of the identified viruses has not been established, this study demonstrates that viral metagenomics is a powerful tool that can be integrated into public-health monitoring efforts to investigate unidentified viruses in cell cultures from clinical isolates where standard PCR assays fail to detect viruses.