Investigation of SARS-CoV-2 Transmission Associated With a Large Indoor Convention - New York City, November-December 2021.

During November 19-21, 2021, an indoor convention (event) in New York City (NYC), was attended by approximately 53,000 persons from 52 U.S. jurisdictions and 30 foreign countries. In-person registration for the event began on November 18, 2021. The venue was equipped with high efficiency particulate air (HEPA) filtration, and attendees were required to wear a mask indoors and have documented receipt of at least 1 dose of a COVID-19 vaccine.* On December 2, 2021, the Minnesota Department of Health reported the first case of community-acquired COVID-19 in the United States caused by the SARS-CoV-2 B.1.1.529 (Omicron) variant in a person who had attended the event (1). CDC collaborated with state and local health departments to assess event-associated COVID-19 cases and potential exposures among U.S.-based attendees using data from COVID-19 surveillance systems and an anonymous online attendee survey. Among 34,541 attendees with available contact information, surveillance data identified test results for 4,560, including 119 (2.6%) persons from 16 jurisdictions with positive SARS-CoV-2 test results. Most (4,041 [95.2%]), survey respondents reported always wearing a mask while indoors at the event. Compared with test-negative respondents, test-positive respondents were more likely to report attending bars, karaoke, or nightclubs, and eating or drinking indoors near others for at least 15 minutes. Among 4,560 attendees who received testing, evidence of widespread transmission during the event was not identified. Genomic sequencing of 20 specimens identified the SARS-CoV-2 B.1.617.2 (Delta) variant (AY.25 and AY.103 sublineages) in 15 (75%) cases, and the Omicron variant (BA.1 sublineage) in five (25%) cases. These findings reinforce the importance of implementing multiple, simultaneous prevention measures, such as ensuring up-to-date vaccination, mask use, physical distancing, and improved ventilation in limiting SARS-CoV-2 transmission, during large, indoor events.†.

Guidelines for Biosafety Training Programs for Workers Assigned to BSL-3 Research Laboratories.

The Guidelines for Biosafety Training Programs for Workers Assigned to BSL-3 Research Laboratories were developed by biosafety professionals who oversee training programs for the 2 national biocontainment laboratories (NBLs) and the 13 regional biocontainment laboratories (RBLs) that participate in the National Institute of Allergy and Infectious Diseases (NIAID) NBL/RBL Network. These guidelines provide a general training framework for biosafety level 3 (BSL-3) high-containment laboratories, identify key training concepts, and outline training methodologies designed to standardize base knowledge, understanding, and technical competence of laboratory personnel working in high-containment laboratories. Emphasis is placed on building a culture of risk assessment-based safety through competency training designed to enhance understanding and recognition of potential biological hazards as well as methods for controlling these hazards. These guidelines may be of value to other institutions and academic research laboratories that are developing biosafety training programs for BSL-3 research.

Autonomous regulation of sex-specific developmental programming in mouse fetal germ cells.

In mice, unique events regulating epigenetic programming (e.g., genomic imprinting) and replication state (mitosis versus meiosis) occur during fetal germ cell development. To determine whether these processes are autonomously programmed in fetal germ cells or are dependent upon ongoing instructive interactions with surrounding gonadal somatic cells, we isolated male and female germ cells at 13.5 days postcoitum (dpc) and maintained them in culture for 6 days, either alone or in the presence of feeder cells or gonadal somatic cells. We examined allele-specific DNA methylation in the imprinted H19 and Snrpn genes, and we also determined whether these cells remained mitotic or entered meiosis. Our results show that isolated male germ cells are able to establish a characteristic "paternal" methylation pattern at imprinted genes in the absence of any support from somatic cells. On the other hand, cultured female germ cells maintain a hypomethylated status at these loci, characteristic of the normal "maternal" methylation pattern in endogenous female germ cells before birth. Further, the surviving female germ cells entered first meiotic prophase and reached the pachytene stage, whereas male germ cells entered mitotic arrest. These results indicate that mechanisms controlling both epigenetic programming and replication state are autonomously regulated in fetal germ cells that have been exposed to the genital ridge prior to 13.5 dpc.

Gradual DNA demethylation of the Oct4 promoter in cloned mouse embryos.

During differentiation, somatic cell nuclei acquire unique patterns of epigenetic modifications, such as DNA methylation, which affect the transcriptional activity of specific genes. Upon transfer into oocytes, however, the somatic nucleus undergoes reprogramming of these epigenetic modifications to achieve pluripotency. Oct4 is one of the critical pluripotency regulators, and is expressed in the germ line, including the pluripotent early embryonic cells. Previous studies showed that the upstream regulatory sequences of the Oct4 gene are distinctly methylated in somatic cells, and the DNA methylation of the regulatory sequences suppresses the transcriptional activity. Thus, successful reprogramming of the somatic cell nucleus to gain pluripotency must be accompanied by the demethylation of the Oct4 regulatory sequences. Here, we investigated the methylation pattern of the Oct4 promoter during early development of cloned mouse embryos. We found that the Oct4 promoter was only gradually demethylated during the early cleavage stages and that the ineffective demethylation of the promoter was associated with developmental retardation. We also found that the upstream sequences of the other pluripotency regulators, namely Nanog, Sox2, and Foxd3, were considerably under-methylated in cumulus cells. These results suggest that the Oct4 gene, as compared to the other pluripotency regulators, needs to undergo extensive demethylation during nuclear reprogramming, and that the failure of such demethylation is associated with inefficient development of cloned somatic cell embryos.

Adult mice cloned from migrating primordial germ cells.

We previously reported that the genomes of gonadal germ cells at 11.5-19.5 days postcoitum (dpc) are incompetent to support full-term development of cloned mouse embryos. In this study, we performed nuclear transfer using primordial germ cells (PGCs) from earlier stages at 8.5-10.5 dpc. When PGC nuclei at 8.5, 9.5, and 10.5 dpc were transferred into enucleated oocytes, seven cloned embryos developed into full-term offspring. Of these, five, all derived from 8.5- or 9.5-dpc PGCs, developed into healthy adults with normal fertility. Of the remaining two offspring derived from 10.5-dpc PGCs, one died shortly after birth, and the other showed slight growth retardation but subsequently developed into a fertile adult. We examined allele-specific methylation at the imprinted H19 and Snrpn loci in 9.5- to 11.5-dpc PGCs. Although the beginning of methylation erasure was evident on the H19 paternal allele at 9.5 dpc, most PGCs did not demonstrate significant erasure of paternal allele-specific methylation until 10.5 dpc. Maternal allele-specific methylation was largely erased from Snrpn by 10.5 dpc. By 11.5 dpc, the majority of PGCs showed nearly complete or complete erasure of allele-specific methylation in both H19 and Snrpn. These results demonstrate that at least some genomic imprints remain largely intact in 8.5- to 9.5-dpc PGCs and then undergo erasure at approximately 10.5 dpc as the PGCs enter the genital ridges. Thus, migrating PGCs at 8.5-9.5 dpc can be successfully used as donors for nuclear transfer, whereas gonadal PGCs at 11.5 dpc and later are incompetent to support full-term development.