EPIDEMIOLOGICAL FEATURES OF COVID-19 FAMILY OUTBREAKS IN CHILDREN

Nicolae Testemitanu State University of Medicine and Pharmacy, Municipal Clinical Hospital of Contagious Diseases in Children


INTRODUCTION
COVID-19 infection has caused huge medical, social and economic impact, rapidly becoming a major public health problem worldwide (1). In 2020, COVID-19 infection control measures largely depended on non-specific prophylactic measures such as: physical distance, hand hygiene, protective masks wear, isolation and quarantine, thus outbreaks investigation became a very important aspect in transmission prevention (2).
The schools were closed in more than 190 countries around the world, affecting 1.57 billion children, and about 90% of the world's student population in the first months of COVID-19 pandemic (3).
The family environment involves close contact and thus a high probability rate of transmission no matter what age or society position (4). The spread of COVID-19 within families is an accelerator of the epidemic. Non-specific prophylactic measures are considered to be effective, but there is little opportunity to support community members reducing the risk of COVID-19 in families (5).
Home isolation measures -implemented as a means in pandemic control have reduced human mobility (6). Thus, the time spent at home increased and SARS-CoV-2 virus transmission in households intensified. Some countries, such as Iceland, have reported a shift in exposure from international travel and social exposure to domestic exposure. In China, the most cases locally generated were detected in households (7).
The studies done to determine the spread of Covid-19 infection in familial outbreaks are useful to obtain clear data on SARS-CoV-2 transmission dynamics and to gain insight into the main determinants (8). Some researches elucidate the role of households/families as one of the most important SARS-CoV-2 infections spread in the population (4,8,9,10). Households will continue to be a significant place for SARS-CoV-2 transmission, as patients with suspected or confirmed SARS-CoV-2 infection are asked to self-isolate at home (10).
A study conducted in China determined that family contacts present the highest risk of transmission, being followed by social and community contacts. Health care contacts constitute the lowest risk, indicating adequate protection measurees for patients and medical staff from Hunan (6). In addition, susceptibility to infection (de-fined as the risk of primary case infection) varies with age: children aged 0-12 are significantly less sensitive than people aged 26-64, but the patients over 65 are much more sensitive (6).
Despite its worldwide spread, COVID-19 epidemiological and clinical patterns remain largely unclear, especially among children (11). Published data on the transmission of SARS-CoV-2 among children in healthcare workers (HCW) families are few (12). A study realized in Spain during the first pandemic wave revealed a high level of SARS-CoV-2 detection in healthcare workers' children, especially when both parents were symptomatic, emphasizing the great impact of family groups in SARS-CoV-2 transmission (12).
Data on contacts epidemiological surveillance in Shenzhen, China, confirmed the role of children in transmitting the infection, with similar data being reported both in children, adults from individual households (13).
Other studies (Netherlands) suggest that SARS-CoV-2 infection is more commonly spread among adults or from adult family members to children (13), especially during the period when schools were closed (13). Family transmission can be conditioned by socio-cultural factors and living conditions; therefore, the results cannot be extrapolated to other populations. Nowadays data on familial transmission of SARS-CoV-2 infection in Western Europe and the role of children in this process are limited (8).
Multiple studies revealed that children of all ages were susceptible to SARS-CoV-2 infection (11). Emerging evidence suggests that young children are at higher risk of COVID-19 than it was initially foreseen (14). Continuous surveillance is needed to understand better the epidemiology, clinical model and transmission of COVID-19 in order to develop effective preventive strategies against COVID-19 in the paediatric population (14).
Several examples of SARS-CoV-2 clusters were linked to a wide range of settings, especially the indoor ones. Few reports came from schools, more from households, and an increasingly high number was reported in hospitals and nursing homes across Europe (10).
Some experts say that the opening of schools, despite the safety measures for symptoms monitoring, personal hygiene, masks wear and distancing among students -did not cause significant outbreaks concerning school (3). However, accumulating the data, it was found that a significant proportion of children and adolescents are asymptomatic or less symptomatic. Summing up can be said that children and adolescents with COVID-19 appear to have higher SARS-CoV-2 viral loads in nasopharyngeal lavage than adults.
Thus, the impact of school opening in diverse epidemiological situations from different communities must be carefully examined (3). Coplex epidemiological studies are needed to determine the role of children in the spread of SARS-CoV-2 infection, returning to organized preschool activities and education at all levels (15).
Study hypothesis: the role of children in SARS-CoV-2 infection transmission was initially underestimated the analysis of the epidemiological features of family outbreaks may highlight the impact of the children in infection spread in these outbreaks.

MATERIAL AND METHODS
The aim of the study was to determine some epidemiological features of COVID-19family outbreaks, emphasizing the impact of the child in the epidemic chain maintenance.
A cross-sectional descriptive observational epidemiological study of 160 family outbreaks sample was performed for this purpose. The primary material used for this research was collected from the clinical observation sheets of the patients diagnosed with COVID-19, who were hospitalized in SCMBCC IMSP, during January-February, 2021. The study involved Covid-19 infection family outbreaks epidemiological features determination. The information was grouped and analysed according to the age of the children, the onset of the disease, the primary sources of the outbreak, the living environment, the children's belonging to communities. The statistical processing of the collected data was performed with the help of Microsoft Excel 2019 program. Statistic assessment was carried out by comparative checking of the studied indices, establishing the statistical threshold of p˂0,05.

RESULTS
To assess the role of the child in the transmission of SARS-CoV-2 infection, we analysed the epidemiological features of COVID-19 in people with family outbreaks. It should be noted that at the stage of this research, in accordance with the provisions of PCN New Corona viral Infection (COVID-19), edition IV, hospitalization was mandatory for all the children with COVID-19, excepting those with asymptomatic forms. The motivation for conducting the study was Covid-19 morbidity decrease in the Republic of Moldova in January (16) and the increase in the number of cases in February (17), during the reopening of educational institutions in January-February 2021.
Out of the total outbreaks analysed for January, it was found that the outbreaks which predominate involved preschool children -45 (62.5%) versus those of school-age children 27 outbreaks (37.5%), there is no statistical difference t=2,09, p˃0,05.
In the group of outbreaks with preschool children -25 (34.72%) were the outbreaks involving children up to 1 year old. Family outbreaks concerning the children up to 1 year came from urban areas in 72% cases (tab. 1).

2020
An important element of our analysis was to determine the primary sources of infection in the family outbreak. Thus, it was established that in infants outbreaks (0-12 months) the first to show signs of disease in about half (52.0%) of cases were parents, in 24.0% of cases the onset of the disease occurred simultaneously in children and parents, which denotes a possible common exposure to the infectious agent, but in other 24.0% of outbreaks -the child was the first to manifest the disease (tab. 2).
In the case of the family outbreaks involving the children aged 1-3 years, analysed for Januarymost came from urban areas, pre-school children accounted 84.61% (tab. 1). Parents' infection was registered in 46.15%, concomitantly in children and parents -46.15%, and the onset of the disease in children -7.70% of outbreaks (tab. 2). In the case of family outbreaks in children aged 4-6 years -the majority (71.42%) of children were organised (tab. 1). The disease started primarily in adults -57.14%, simultaneously in adults and children -14.29% of cases, and in 28.57% the child became ill first (tab. 2).
Generally, in the focus group involving preschool children, hospitalized in January (tab. 2), the first to show signs of COVID-19 were the adults (parents or caregivers) -51.11%, concomitant onset of the disease -28.89% and in only 20.0% of outbreaks the child was the primary infected family member.
Among the outbreaks in school-age children, the highest percentage (70.37%) was in children aged 11 and more. The majority (84.21%) of chil-dren were organized, from urban areas (tab. 1). The first in the family to get infected were the adults about 1/2 (52.63%) of cases; in 47.36%the children were the first to show clinical signs (tab. 2).
An interesting element is the fact that in schoolage children outbreaks, the children hospitalized in January, were the first to manifest the disease being the primary sources of infection in families -13 outbreaks (48.15%), in other 12 outbreaks (44.44%) -the parents were initially affected, and in only 2 outbreaks (7.40%) the onset of the disease was concomitant both in children and adults (tab. 2).
Analysing the data for January it was determined that 81.9% of the total outbreaks were from urban areas in 43.05% of outbreaks (tab. 1). The adults were predominantly registered as primary sources of infection in the family (48,61%) or concomitant illness was observed (20.83% of outbreaks), which does not exclude common exposure to the source of infection. Only in 30.56% outbreaks the onset of the disease was primarily reported to affect children (tab. 2).  were the first to get ill in 53.84% of outbreaks, in 23.08% of outbreaks the adults were the first to get infected -or concomitant infection occurred (tab. 4).
In school-age children outbreaks -53.19% of cases the child was the first to manifest the disease, 40.42% -the first to become infected were the parents, but in 6.38% outbreaks -the disease was concomitant (tab. 4). Data accumulation and analysis proved that a percentage of asymptomatic or symptomatic children can be significant (18). Moreover, children and adolescents with COVID-19 have higher viral loads than adults do in the early stages of 2020 the disease (19,20,21). Schools and kindergartens closure and reopening is a major issue of education, politics and public health worldwide. There are concerns about the transmission of SARS-CoV-2 virus among children and teachers in the school environment (3).
At the same time, there are limited data on transmission among children that could lead to major outbreaks, especially in school. A systematic review suggested that children are unlikely to be the most important factors in COVID-19 pandemic (22). It is unclear whether the dynamics of the virus transmission in the paediatric population differs from that of adults, or this may be because most schools remain closed for extended periods there may be other factors that need exploration.
However, the most common sources of infection for paediatric cases of COVID-19 appear to be members of their adult family according to some studies children are not the primary source of infection and have not caused major outbreaks in communities (23). Referring to our results, where children were the source of infection in their families there is a significant number of outbreaks, thus we can conclude that they are involved in catalysing the epidemic process in SARS-CoV-2 virus infection.
Our study suggests the need to apply antiepidemic measures to the child population. Proper masks wear is a way to reduce the spread of the virus in the community by stopping its spread through respiratory secretions from sources of infection, including children. Wearing protective masks in public, children can help stop the spread of COVID-19 -and to protect their families, communities and themselves.
The teachers in institutions can be exposed to a much higher risk of infection with SARS-CoV-2 virus, interacting with children who are an important source of infection. Teachers' protection and prevention from SARS-CoV-2 viral infection is vaccination.
This entails close epidemiological surveillance of children, especially adolescents, taking into account their increased potential for infection outside family outbreaks. In this context, the results of our study are consistent with previously published studies (24).

The number of outbreaks requiring hospitalization at Municipal Clinical Hospital of Contagious
Diseases in Children increased in February compared to January.