How One Meat Processing Plant Worker May Have Infected 1400 Colleagues
Detailed investigation of a superspreading event in a meat processing plant in Germany:
Background
Here, we describe a multifactorial investigation of the events of a SARS-CoV-2 outbreak in the largest meat processing complex in Germany.
Methods
Timing of infection events, spatial relationship between workers in the meat processing plant, climate and ventilation conditions, sharing of living quarters and transport, and full viral genome sequences recovered from PCR-confirmed SARS-CoV-2 cases were analyzed.
Findings
Transmissions occurred in a confined area of a meat processing plant in which air is constantly re-circulated and cooled to 10°C. Index case B1 transmitted the virus to co-workers in a radius of more than 8 meters during work-shifts on 3 consecutive days. Assessment of viral sequences shows that all cases share a set of eight single nucleotide mutations representing a novel sub-branch in the SARS-CoV-2 C20 clade. We identified the same set of mutations in samples collected in the time period between the initial infection cluster and a subsequent outbreak in the following month, with the largest number of confirmed SARS-CoV-2 positive cases in a meat processing facility reported so far.
Here, we describe a multifactorial investigation of the events of a SARS-CoV-2 outbreak in the largest meat processing complex in Germany.
Methods
Timing of infection events, spatial relationship between workers in the meat processing plant, climate and ventilation conditions, sharing of living quarters and transport, and full viral genome sequences recovered from PCR-confirmed SARS-CoV-2 cases were analyzed.
Findings
Transmissions occurred in a confined area of a meat processing plant in which air is constantly re-circulated and cooled to 10°C. Index case B1 transmitted the virus to co-workers in a radius of more than 8 meters during work-shifts on 3 consecutive days. Assessment of viral sequences shows that all cases share a set of eight single nucleotide mutations representing a novel sub-branch in the SARS-CoV-2 C20 clade. We identified the same set of mutations in samples collected in the time period between the initial infection cluster and a subsequent outbreak in the following month, with the largest number of confirmed SARS-CoV-2 positive cases in a meat processing facility reported so far.
[...]
Our findings indicate that a physical distance of 2 meters does not suffice to prevent transmission in environmental conditions such as those studied here; additional measures such as improved ventilation and airflow, installation of filtering devices or use of high-quality face masks are required to reduce the infection risk in these environments.
Discussion
Our results collectively point towards a superspreading event in the MPP-R beef processing plant that originated from a single employee. Our findings suggest that the facilities’ environmental conditions, including low temperature, low air exchange rates, and constant air re-circularization, together with relatively close distance between workers and demanding physical work, created an unfavorable mix of factors promoting efficient aerosol transmission of SARS-CoV-2 particles. It is very likely that these or similar factors are also responsible for current worldwide ongoing outbreaks in other meat or fish processing facilities. The recurrent emergence of such outbreaks suggests that employees in meat or fish processing facilities need to be frequently and systematically screened to prevent future SARS-CoV-2 outbreaks. Furthermore, immediate action needs to be taken to quarantine all workers in a radius around an infected individual that may significantly extend beyond 2m. Importantly, while we observed transmission in a ~8m area, exact transmission distances are likely to vary substantially depending on facility layout and operation conditions. Additional studies are therefore required to determine the most important parameters which may be altered to lower infection risk, for example via optimization of airflow or ventilation conditions.
In contrast to work-related exposure, shared apartments, bedrooms, or carpools appear not to have played a major role in the initial outbreak described in this study. Nevertheless, later viral transmission within shared living quarters or work rides very well may have been a confounding factor in context of the second, larger outbreak occurring one month after the first outbreak. Our genotyping results are fully compatible with the hypothesis that this second outbreak was seeded by cases related to the initial cluster.
In contrast to work-related exposure, shared apartments, bedrooms, or carpools appear not to have played a major role in the initial outbreak described in this study. Nevertheless, later viral transmission within shared living quarters or work rides very well may have been a confounding factor in context of the second, larger outbreak occurring one month after the first outbreak. Our genotyping results are fully compatible with the hypothesis that this second outbreak was seeded by cases related to the initial cluster.
[...]
In conclusion, this study indicates that transmission of SARS-CoV-2 can occur over distances of at least 8m in confined spaces under conditions of relatively low air exchange rates and high rates of recirculated unfiltered air. The significance of this study is imminent for the meat and fish processing industry but might well reach beyond these industries, and points to the importance of air quality/flow in confined spaces to prevent future superspreading events.