A mixed-methods approach to elucidate SARS-CoV-2 transmission routes and clustering in outbreaks in native workers and labour migrants in the fruit and vegetable packaging industry in South Holland, the Netherlands, May to July 2020.

OBJECTIVES: To obtain insight into SARS-CoV-2 clustering and transmission routes during outbreaks in the predominantly migrant workforce of the fruit and vegetable packaging industry of South Holland, the Netherlands, May to July 2020. DESIGN: This mixed-methods study applied direct observation and interviews, epidemiologic investigation, source and contact data analysis and whole-genome sequencing. RESULTS: We detected 46 SARS-CoV-2 cases and 4 outbreaks with a proportional representation of labour migrant and native workers in 6 unrelated facilities. Complete viral genome sequences revealed at least 3 clusters of native workers and labour migrants, 2 within and 1 between facilities. On-site inspections found adequate implementation of preventative measures to which both native workers and labour migrants showed suboptimal adherence. Being a labour migrant was associated with living in shared housing, but not with more contacts or different sources. CONCLUSIONS: The fruit and vegetable packaging industry gave the impression of sufficient preparedness and control. Suboptimal adherence to the facilities' preventative guidelines could have facilitated work floor transmission. Community and household transmission are likely to have contributed to outbreaks. We encourage further research into risk factors for transmission in labour migrants and application of these insights into targeted public health policy.

Measuring the depth of invasion in vulvar squamous cell carcinoma: interobserver agreement and pitfalls.

AIMS: The depth of invasion is an important prognostic factor for patients with vulvar squamous cell carcinoma (SCC). The threshold of 1 mm distinguishes between FIGO stages IA and ≥IB disease and guides the need for groin surgery. Therefore, high interobserver agreement is crucial. The conventional and the alternative method are described to measure the depth of invasion. The aims of this study were to assess interobserver agreement for classifying the depth of invasion using both methods and to identify pitfalls. METHODS AND RESULTS: Fifty slides of vulvar SCC with a depth of invasion approximately 1 mm were selected, digitally scanned and independently assessed by 10 pathologists working in a referral or oncology centre and four pathologists in training. The depth of invasion was measured using both the conventional and alternative method in each slide and categorised into ≤1 and >1 mm. The percentage of agreement and Light's kappa for multi-rater agreement were calculated, and 95% confidence intervals were calculated by bootstrapping (1000 runs). The agreement using the conventional method was moderate (κ = 0.57, 95% confidence interval = 0.45-0.68). The percentage of agreement among the participating pathologists using the conventional method was 85.0% versus 89.4% using the alternative method. Six pitfalls were identified: disagreement concerning which invasive nest is deepest, recognition of invasive growth and where it starts, curved surface, carcinoma situated on the edge of the tissue block, ulceration and different measurement methods. CONCLUSIONS: Pathologists reached only moderate agreement in determining the depth of invasion in vulvar SCC, without a notable difference between the two measurement methods.

Fluctuation of Viremia in Hepatitis B Virus-Infected Healthcare Workers Performing Exposure-Prone Procedures in the Netherlands.

OBJECTIVE: To determine the longitudinal changes in viral load of hepatitis B virus (HBV)-infected healthcare workers (HCWs) and its consequences for exclusion of infected HCWs performing exposure-prone procedures, various HBV DNA safety thresholds, and the frequency of monitoring. DESIGN: Retrospective cohort study June 1, 1996-January 31, 2013. Participants In the Netherlands, chronically HBV-infected HCWs performing exposure-prone procedures are notified to the Committee for Prevention of Iatrogenic Hepatitis B. Of the 126 notified HCWs, 45 had 2 or more HBV DNA levels determined without antiviral therapy. METHODS: A time-to-event analysis for HBV-infected HCWs categorized in various viremia levels surpassing a HBV DNA threshold level of 1×105 copies/mL, above which exposure-prone procedures are not allowed in the Netherlands. RESULTS: Fluctuations of HBV DNA in follow-up samples ranged from -5.4 to +2.2 log10 copies/mL. A high correlation was seen for each HBV DNA level with the 3 previous levels. In a time-to-event analysis, after 6 months 7.2%, 6.5%, and 14.3% of individuals had surpassed the threshold of 1×105 copies/mL for viral load categories 4.8×103 to 1.5×104; 1.5×104 to 4.0×104; and 4.0×104 to 1.0×105, respectively. CONCLUSIONS: We propose standard retesting every 6 months, with more frequent retesting just below the high threshold value (1×105 copies/mL), and prolonging this standard interval to 1 year after 3 consecutive levels below the threshold in policies with lower safety thresholds (1×103 or 1×104 copies/mL). Infect Control Hosp Epidemiol 2016;37:655-660.