Аэрозольный способ передачи
Довольно показательное исследование про заразность ковида, на примере бельгийского дома для престарелых.
В заведении 179 жителей, и с начала эпидемии до ноября 2020 года у них было 11 случаев (осенью), выявленных регулярным скринингом, асимптоматичных, которые изолировали, ссоблюдением всех протоколов итп.
Но к зиме карантин уже сняли, тк вроде бы уже побороли эпидемию, да и локальные случаи, и провели культурно массовое мероприятие, в декабре- волонтер извне, наряженный как легендарный персонаж, принес подарки, поздравил и тд, посетив все 4 здания комплекса (большие комнаты для сбора народа). Время присутствия волонтера в помещении было не особо долгим- 20-30 минут, но этого хватило. К сожалению, через день после мероприятия волонтер почувствовал себя неважно и протестировался- оказался ковид, причем с высоким выделением вируса- менее 13.5 циклов ПЦР для определения..
В ближайшее время после этого социального мероприятия, в доме престарелых подхватило ковид 115 человек, к концу декабря- уже127 жителей и 40 сотрудников (все сотрудники имели негативные тесты на момент социального мероприятия с волонтером, 4 дневной давности), и уже были умершие от ковида. Судя по времени, когда началась вспышка- это все складывалось в передачу от этого волонтера, и родство штамма подтвердил генетический анализ образцов от всех участников вспышки.
Среди заболевших ковидом стариков, 61% были выраженно симптоматичны, и 35 человек умерло из-за этой вспышки (те. 28% смертность, на примере выборки). Наиболее активно начали заболевать на 6 день после мероприятия. Переболевшие асимптоматично в октябре, кстати, заразились с такой же частотой, и примерно в те же сроки, как и не болешие ковидом до этой вспышки.
Кто старше 80 и женщины были более уязвимы.
Авторы пришли к выводу, что заражение произошло по воздуху, аэрозольно, тк все происходило в (плохо) кондиционируемом помещении, и заразились не только те, кто был рядом (на уровне социальной дистанции) да и вообще на этом мероприятии, но и в других помещениях (35%), причем примерно в тех же сроки. Т.е вирус либо распространился через общий воздух, либо персистировал достаточное время в достаточном количестве (тк вентиляция была неважной) в помещении которое посетил волонтер, и этого оказалось достаточно для такой массивной вспышки (суперраспространение).
Abstract Objectives: To better understand the conditions which have led to one of the largest COVID-19 outbreaks in Belgian nursing homes in 2020. Setting: A nursing home in Flanders, Belgium, which experienced a massive outbreak of COVID-19 after a cultural event. An external volunteer who dressed as a legendary figure visited consecutively the 4 living units and tested positive for SARS-CoV-2 the next day. Within days, residents started to display symptoms and the outbreak spread rapidly within the nursing home. Methods: We interviewed key informants and collected standardized data from all residents retrospectively. A batch of 115 positive samples with a Ct value of <37 by qRT-PCR were analysed using whole-genome sequencing. Six months after the outbreak, ventilation assessment of gathering rooms in the nursing home was done using a tracer gas test with calibrated CO2 sensors.
An external volunteer who dressed as a legendary figure visited consecutively four rooms where residents of living units A, B and C were gathered. Three staff members, of whom two were dressed up as helpers to hand out gifts, were part of the company. Visits lasted from 15 to 30 minutes per room. Finally, the company strolled through the corridor of unit “D”whose residents remained in their rooms. Because of confidentiality concerns, a detailed description of the event and flow of the visit is not published here, but is available upon request. The sequence of events related to the outbreak is summarized in Figure 1. All staff had tested negative on the last monthly screening four days before the outbreak. The social event, with the visit of the volunteer, toke placeon day 0(Event). The residents of Unit “D” werein quarantine on day0, because one resident of the unit,while in hospital,had tested positive a few days before.All residents of unit “D” tested negative onday0. One day later, the volunteer developedsymptoms and testedpositive for SARS-CoV-2 with Ct values < 13.5 for all three target genescategorized as “very high viral load”.A first resident (from unit“A”)startedhavingsymptoms suggestive ofCOVID-19 fourdays after the event. Selected testing was initiated, mostlyguided by symptoms, followed by rounds of general testing (details see Figure 1). Because of the fear of an emerging outbreak, all residents were confined totheir rooms. The infected residents were cared for in dedicated COVID-19sections of the nursing home, and additionalprotective equipmentfor the nursing staff was made available. The proportion of positive tests was35.6%, 42.0%, 26.4%, 16.2%and8.8%, on respectivelyday 7, 10, 14, 19 and 26 after the event. On day 9 afirst resident died of COVID-19. By the end of December,a total of 127residents and 40 staff were diagnosed with SARS-CoV-2since the beginning of the outbreak.Among the infectedresidents, 77 experienced COVID-19 symptoms (60.6%) and 35 died, resulting in a case fatality rate of 27.6%. he 115 samples for genotyping were collected at an early stage in the epidemic and originated from 97 residents, 17 staff and 1 (external) volunteer. Ct valueswere< 40 for all three target genes.All 115 SARS-CoV-2 sequencescould be assigned to clade 20B according to Nextclade, while phylogenetically the lineage B.1.1 was derived. Phylogenetic inference (see Figure 2) of a large set of publicly available B.1.1 genomes clearly depicts the presence of one large cluster, embedding all sequences of the outbreak, providing evidence of one circulating strain. Except for a limited number of point mutations, sequences were found to be identical, suggesting a single source outbreak. Apart from the amino acid substitution D614G, a mutation that is prevalent in nearly all Belgian SARS-CoV-2 genomes since the start of the epidemic,no changes were reported in the Spike protein compared to Wuhan reference NC_045512 (9) By the end of the outbreak,127 (77%)residents had tested positive, and the attack rates differedbyliving unit(see Figure 3). The steepestincrease was seen aroundday 6 inthe3 units participating in the event(“A”, “B”and “C”).In unit “D”the main increase of infections was seen on day 10.The cumulative attack rate of unit “D”also remained lower:52.5 % as compared to the other units:84.5%,92.1%and 77.8% in respectively living unit“A”, “B”and “C”.At the time of theevent, there were 124 women (75.2%) and 41 men (24.8%) residing in “Z”. The median age was 87 years old, IQR 82-91,with a minimum of 62 and a maximum of 100 years. A total of 97 residents out of the 165 (88.7%) participated in the event.Attack rates were higher among female residents, and among residents older than 80 years, albeit not significantly.Nine residents who experienced anasymptomatic SARS-CoV-2 infection in October 2020 did not have a lower attack rate.Participation in the event was theonly variablesignificantly associatedwith a higher attack rate (Table 1).Living unit was not included in the multivariable analysis, because of collinearitywith presence atthe event (none of the residents of unit “D” were present in a gathering room). We assumed infections detected within 8 days of the event were likely directly linked to the event and defined them as early infections. Participation in the event was associated with higherearly infection rates, but some residents who had not participated in the eventwere also early infected. Among the 97 residents who were present at the event, 86 (88.7%) became infected with SARS-CoV-2. Of these 86 infections, 45 (52.3%) were detected within 8 days. Among the 68 residents who were not present at the event, 41 (60.3%) became infected with SARS-CoV-2. Of these 41 infections, 14 (34.1%) were detected within 8 days. More detailed information on the timing of SARS-CoV-2 diagnoses and attendance at the event by living unit is shown in Supplementary Figure 1. Risk factors for early infectionamong the97 residentswho participated in the eventwere further exploredin a nested case control analysis.Cases were residents whoparticipated in the event and tested positive within 8 days after the event (N=45), andcontrols were residents who participated in the event but remained negative or tested positive after 14 days or later(N=20).Gathering room, distance tothe volunteer, wearing of a maskorcontact with the volunteerwere not associated with early infection. Only having had contact with ahelperwas associated with early infection(OR = 5.86, 95%CI:1.36-30.81)(Table 2)Our investigation shows a rapid and widespread outbreak of SARS-CoV-2 in a nursing home with an identical viruspointing to a single source. The virus wasmost likely introducedinto the nursing homeby the volunteer and amplified by the social event. Aerosol transmissionin crowded poorly ventilated spaces isthe most plausible explanation for the massive intra-facilityspread.Severe outbreaksof COVID-19in nursing homes have been reportedall over the world throughout 2020. The attack rate of 77% among 165 residents in this study ismuch higher than attack rates previously reported in nursing homes during thesame, pre-vaccination, period. This very high attack rateis worrisome. Especially when considering the many measures which were put in place to prevent the spread of Covid-19, including continuousinfection control measures for staff, the ban of visitors andtheimplementation of room quarantineand cohorting ofinfected residents.Based on the timeline of diagnoses and symptomonsets, and the significant association we found between infection and presence at the event, we can point to the cultural event as the most plausible start of the outbreak. Thevolunteer was pre-symptomatic with avery high viral loadon the day of the eventand had contact with the fourunits of the nursing homeduring the same day. He was also the first to develop COVID-related symptoms, and therefore most likelythe index case. Introduction of the virus by a staff member during the same periodcannot be excluded butis unlikely, as most of the staff were confined to one unitand all of themtested negative during a routine testing fourdays beforethe event. One of thehelpersof the volunteertested positive on day8 butstarted having symptoms only after a few days. It is very unlikely that this person was already infectious on the day of the event. Theassociation we found between early infection and contact with a helper remains unexplained. The large majority of residents participating in the event had a brief contact with a helper when he/she handed out a present. In the absence of other valid hypotheses, we think this association was a random finding, also taking into account the very small number of residents whodid not have a contact with a helper. It is well established thatSARS-CoV-2 is readily transmitted in indoor environments(11-13).Airborne transmission hasbeing recognized as an important route of transmission(14,15).Wehave severalarguments to support the dominance of airborne transmissionin this outbreak.First of all, the social event was typically a crowdedprolongedindoor happening ingathering rooms with no adequate ventilation. In addition, mask wearing was sub-optimal. The long beard of the volunteer made it difficult to effectively fit the surgical mask, and manyresidents were not wearing masks.Furthermore,we could not demonstrate the role of direct contact or droplets in this outbreak. Indeed, among those present at the event, the case control study showed no association between early infection and distance to or contact with the volunteer. Finally, the fact that some residents not present at the event were early infected may seempuzzling, but canalso point to long-range aerosol transmission. The gathering rooms were connected by corridors where residents stroll. Moreover, some residentswho did not participate in the eventtook a coffee in the same room shortly after the event. The virus may have spread through aerosols as long as three hours after the event (16). Taken the previous into account, ventilation may play a key role in the control of SARS-CoV-2. Our measurements indicate a rather poor ventilation quality in the nursing home. Background CO2concentrations in the assessed rooms (average 657 ppm to 846 ppm) were considerably higher than would be expected for a well-ventilatedroom with low or no occupancy.Taking into accountthe rural environment of the nursing home, one would expect an average outdoor CO2concentration between 400-450 ppm, and thus expecting an equal background level inside the rooms. In addition, measurements took place in summer time, with exterior doors and windows open, probably resulting in lower CO2concentrations than the concentration at the time of the event. The Belgian national guidelines for COVID-19 prevention recommend indoor CO2-levels of maximum 900 ppm (or a fresh air supply of 40 m³/h per person) (https://www.info-coronavirus.be/en/ventilation/). In addition, none ofthe rooms assessed reached the latest recommendations from the Federation of European Heating, Ventilation and Air Conditioning Associations (REHVA) nor the ventilation rates suggested in the interim guide on COVID-19 infection prevention and control during health careof the World Health Organization (WHO)(18,19). On the other hand, if heating, ventilation and air conditioning systems are not correctly used, they may contribute to the transmission/spreading of airborne diseases as demonstrated in the past for SARS (20). In the largest room during the event,the only air treatment systemwas a fan coil unit, a device that uses acoiland afanto heat or cool a room without outdoor air supply. Indoor air moves over thecoil, which heats or cools the air before pushing it back out into the room. To prevent the spread of an airborne virus, the use of such installations is highly dissuaded since instead of diluting indoor concentration, they distribute potential infectious particles in a room.
В заведении 179 жителей, и с начала эпидемии до ноября 2020 года у них было 11 случаев (осенью), выявленных регулярным скринингом, асимптоматичных, которые изолировали, ссоблюдением всех протоколов итп.
Но к зиме карантин уже сняли, тк вроде бы уже побороли эпидемию, да и локальные случаи, и провели культурно массовое мероприятие, в декабре- волонтер извне, наряженный как легендарный персонаж, принес подарки, поздравил и тд, посетив все 4 здания комплекса (большие комнаты для сбора народа). Время присутствия волонтера в помещении было не особо долгим- 20-30 минут, но этого хватило. К сожалению, через день после мероприятия волонтер почувствовал себя неважно и протестировался- оказался ковид, причем с высоким выделением вируса- менее 13.5 циклов ПЦР для определения..
В ближайшее время после этого социального мероприятия, в доме престарелых подхватило ковид 115 человек, к концу декабря- уже127 жителей и 40 сотрудников (все сотрудники имели негативные тесты на момент социального мероприятия с волонтером, 4 дневной давности), и уже были умершие от ковида. Судя по времени, когда началась вспышка- это все складывалось в передачу от этого волонтера, и родство штамма подтвердил генетический анализ образцов от всех участников вспышки.
Среди заболевших ковидом стариков, 61% были выраженно симптоматичны, и 35 человек умерло из-за этой вспышки (те. 28% смертность, на примере выборки). Наиболее активно начали заболевать на 6 день после мероприятия. Переболевшие асимптоматично в октябре, кстати, заразились с такой же частотой, и примерно в те же сроки, как и не болешие ковидом до этой вспышки.
Кто старше 80 и женщины были более уязвимы.
Авторы пришли к выводу, что заражение произошло по воздуху, аэрозольно, тк все происходило в (плохо) кондиционируемом помещении, и заразились не только те, кто был рядом (на уровне социальной дистанции) да и вообще на этом мероприятии, но и в других помещениях (35%), причем примерно в тех же сроки. Т.е вирус либо распространился через общий воздух, либо персистировал достаточное время в достаточном количестве (тк вентиляция была неважной) в помещении которое посетил волонтер, и этого оказалось достаточно для такой массивной вспышки (суперраспространение).
Abstract Objectives: To better understand the conditions which have led to one of the largest COVID-19 outbreaks in Belgian nursing homes in 2020. Setting: A nursing home in Flanders, Belgium, which experienced a massive outbreak of COVID-19 after a cultural event. An external volunteer who dressed as a legendary figure visited consecutively the 4 living units and tested positive for SARS-CoV-2 the next day. Within days, residents started to display symptoms and the outbreak spread rapidly within the nursing home. Methods: We interviewed key informants and collected standardized data from all residents retrospectively. A batch of 115 positive samples with a Ct value of <37 by qRT-PCR were analysed using whole-genome sequencing. Six months after the outbreak, ventilation assessment of gathering rooms in the nursing home was done using a tracer gas test with calibrated CO2 sensors.
An external volunteer who dressed as a legendary figure visited consecutively four rooms where residents of living units A, B and C were gathered. Three staff members, of whom two were dressed up as helpers to hand out gifts, were part of the company. Visits lasted from 15 to 30 minutes per room. Finally, the company strolled through the corridor of unit “D”whose residents remained in their rooms. Because of confidentiality concerns, a detailed description of the event and flow of the visit is not published here, but is available upon request. The sequence of events related to the outbreak is summarized in Figure 1. All staff had tested negative on the last monthly screening four days before the outbreak. The social event, with the visit of the volunteer, toke placeon day 0(Event). The residents of Unit “D” werein quarantine on day0, because one resident of the unit,while in hospital,had tested positive a few days before.All residents of unit “D” tested negative onday0. One day later, the volunteer developedsymptoms and testedpositive for SARS-CoV-2 with Ct values < 13.5 for all three target genescategorized as “very high viral load”.A first resident (from unit“A”)startedhavingsymptoms suggestive ofCOVID-19 fourdays after the event. Selected testing was initiated, mostlyguided by symptoms, followed by rounds of general testing (details see Figure 1). Because of the fear of an emerging outbreak, all residents were confined totheir rooms. The infected residents were cared for in dedicated COVID-19sections of the nursing home, and additionalprotective equipmentfor the nursing staff was made available. The proportion of positive tests was35.6%, 42.0%, 26.4%, 16.2%and8.8%, on respectivelyday 7, 10, 14, 19 and 26 after the event. On day 9 afirst resident died of COVID-19. By the end of December,a total of 127residents and 40 staff were diagnosed with SARS-CoV-2since the beginning of the outbreak.Among the infectedresidents, 77 experienced COVID-19 symptoms (60.6%) and 35 died, resulting in a case fatality rate of 27.6%. he 115 samples for genotyping were collected at an early stage in the epidemic and originated from 97 residents, 17 staff and 1 (external) volunteer. Ct valueswere< 40 for all three target genes.All 115 SARS-CoV-2 sequencescould be assigned to clade 20B according to Nextclade, while phylogenetically the lineage B.1.1 was derived. Phylogenetic inference (see Figure 2) of a large set of publicly available B.1.1 genomes clearly depicts the presence of one large cluster, embedding all sequences of the outbreak, providing evidence of one circulating strain. Except for a limited number of point mutations, sequences were found to be identical, suggesting a single source outbreak. Apart from the amino acid substitution D614G, a mutation that is prevalent in nearly all Belgian SARS-CoV-2 genomes since the start of the epidemic,no changes were reported in the Spike protein compared to Wuhan reference NC_045512 (9) By the end of the outbreak,127 (77%)residents had tested positive, and the attack rates differedbyliving unit(see Figure 3). The steepestincrease was seen aroundday 6 inthe3 units participating in the event(“A”, “B”and “C”).In unit “D”the main increase of infections was seen on day 10.The cumulative attack rate of unit “D”also remained lower:52.5 % as compared to the other units:84.5%,92.1%and 77.8% in respectively living unit“A”, “B”and “C”.At the time of theevent, there were 124 women (75.2%) and 41 men (24.8%) residing in “Z”. The median age was 87 years old, IQR 82-91,with a minimum of 62 and a maximum of 100 years. A total of 97 residents out of the 165 (88.7%) participated in the event.Attack rates were higher among female residents, and among residents older than 80 years, albeit not significantly.Nine residents who experienced anasymptomatic SARS-CoV-2 infection in October 2020 did not have a lower attack rate.Participation in the event was theonly variablesignificantly associatedwith a higher attack rate (Table 1).Living unit was not included in the multivariable analysis, because of collinearitywith presence atthe event (none of the residents of unit “D” were present in a gathering room). We assumed infections detected within 8 days of the event were likely directly linked to the event and defined them as early infections. Participation in the event was associated with higherearly infection rates, but some residents who had not participated in the eventwere also early infected. Among the 97 residents who were present at the event, 86 (88.7%) became infected with SARS-CoV-2. Of these 86 infections, 45 (52.3%) were detected within 8 days. Among the 68 residents who were not present at the event, 41 (60.3%) became infected with SARS-CoV-2. Of these 41 infections, 14 (34.1%) were detected within 8 days. More detailed information on the timing of SARS-CoV-2 diagnoses and attendance at the event by living unit is shown in Supplementary Figure 1. Risk factors for early infectionamong the97 residentswho participated in the eventwere further exploredin a nested case control analysis.Cases were residents whoparticipated in the event and tested positive within 8 days after the event (N=45), andcontrols were residents who participated in the event but remained negative or tested positive after 14 days or later(N=20).Gathering room, distance tothe volunteer, wearing of a maskorcontact with the volunteerwere not associated with early infection. Only having had contact with ahelperwas associated with early infection(OR = 5.86, 95%CI:1.36-30.81)(Table 2)Our investigation shows a rapid and widespread outbreak of SARS-CoV-2 in a nursing home with an identical viruspointing to a single source. The virus wasmost likely introducedinto the nursing homeby the volunteer and amplified by the social event. Aerosol transmissionin crowded poorly ventilated spaces isthe most plausible explanation for the massive intra-facilityspread.Severe outbreaksof COVID-19in nursing homes have been reportedall over the world throughout 2020. The attack rate of 77% among 165 residents in this study ismuch higher than attack rates previously reported in nursing homes during thesame, pre-vaccination, period. This very high attack rateis worrisome. Especially when considering the many measures which were put in place to prevent the spread of Covid-19, including continuousinfection control measures for staff, the ban of visitors andtheimplementation of room quarantineand cohorting ofinfected residents.Based on the timeline of diagnoses and symptomonsets, and the significant association we found between infection and presence at the event, we can point to the cultural event as the most plausible start of the outbreak. Thevolunteer was pre-symptomatic with avery high viral loadon the day of the eventand had contact with the fourunits of the nursing homeduring the same day. He was also the first to develop COVID-related symptoms, and therefore most likelythe index case. Introduction of the virus by a staff member during the same periodcannot be excluded butis unlikely, as most of the staff were confined to one unitand all of themtested negative during a routine testing fourdays beforethe event. One of thehelpersof the volunteertested positive on day8 butstarted having symptoms only after a few days. It is very unlikely that this person was already infectious on the day of the event. Theassociation we found between early infection and contact with a helper remains unexplained. The large majority of residents participating in the event had a brief contact with a helper when he/she handed out a present. In the absence of other valid hypotheses, we think this association was a random finding, also taking into account the very small number of residents whodid not have a contact with a helper. It is well established thatSARS-CoV-2 is readily transmitted in indoor environments(11-13).Airborne transmission hasbeing recognized as an important route of transmission(14,15).Wehave severalarguments to support the dominance of airborne transmissionin this outbreak.First of all, the social event was typically a crowdedprolongedindoor happening ingathering rooms with no adequate ventilation. In addition, mask wearing was sub-optimal. The long beard of the volunteer made it difficult to effectively fit the surgical mask, and manyresidents were not wearing masks.Furthermore,we could not demonstrate the role of direct contact or droplets in this outbreak. Indeed, among those present at the event, the case control study showed no association between early infection and distance to or contact with the volunteer. Finally, the fact that some residents not present at the event were early infected may seempuzzling, but canalso point to long-range aerosol transmission. The gathering rooms were connected by corridors where residents stroll. Moreover, some residentswho did not participate in the eventtook a coffee in the same room shortly after the event. The virus may have spread through aerosols as long as three hours after the event (16). Taken the previous into account, ventilation may play a key role in the control of SARS-CoV-2. Our measurements indicate a rather poor ventilation quality in the nursing home. Background CO2concentrations in the assessed rooms (average 657 ppm to 846 ppm) were considerably higher than would be expected for a well-ventilatedroom with low or no occupancy.Taking into accountthe rural environment of the nursing home, one would expect an average outdoor CO2concentration between 400-450 ppm, and thus expecting an equal background level inside the rooms. In addition, measurements took place in summer time, with exterior doors and windows open, probably resulting in lower CO2concentrations than the concentration at the time of the event. The Belgian national guidelines for COVID-19 prevention recommend indoor CO2-levels of maximum 900 ppm (or a fresh air supply of 40 m³/h per person) (https://www.info-coronavirus.be/en/ventilation/). In addition, none ofthe rooms assessed reached the latest recommendations from the Federation of European Heating, Ventilation and Air Conditioning Associations (REHVA) nor the ventilation rates suggested in the interim guide on COVID-19 infection prevention and control during health careof the World Health Organization (WHO)(18,19). On the other hand, if heating, ventilation and air conditioning systems are not correctly used, they may contribute to the transmission/spreading of airborne diseases as demonstrated in the past for SARS (20). In the largest room during the event,the only air treatment systemwas a fan coil unit, a device that uses acoiland afanto heat or cool a room without outdoor air supply. Indoor air moves over thecoil, which heats or cools the air before pushing it back out into the room. To prevent the spread of an airborne virus, the use of such installations is highly dissuaded since instead of diluting indoor concentration, they distribute potential infectious particles in a room.