Discussion

The new coronavirus, named SARS-CoV-2, is the cause of COVID-19. The WHO characterized this disease as a pandemic on March 11, 2020. ⁵ Until the final data collection date for this research, Brazil had already become the second country with the highest number of cases in the world. ⁶ With little evidence and reports on COVID-19 in children, this disease is a challenge in the pediatric population. ^{7,Reference Dong, Mo and Hu8} Some research indicates that children become viral reservoirs, as they are important in the transmission cycle of COVID-19 (SARS-CoV-2) to the community. ^{Reference Brodin9–Reference See, Liew and Ng11}

The last 10 to 15 years have taught us that respiratory viruses are ‘not only’ causes of infections of the upper airways, but also infections of the lower airways. ^{Reference Jain, Self and Wunderink12,Reference Machado13} Influenza, parainfluenza, adenovirus, and respiratory syncytial virus, as well as rhinovirus, and SARS-CoV, should be included as a differential diagnosis for SARS-CoV-2. There is also the possibility of the coexistence of viruses or even bacteria in COVID-19. ^{6,Reference Xia, Shao and Guo14}

WHO declared that most Brazilian children have about 4 to 6 acute respiratory infections per year, directly impacting public health. ^{Reference Henschel and Chan15} Besides, Nunes et al. ^{Reference Nunes16} point out that in most cases, COVID-19 resembles the common flu, and other people will fall into the class of asymptomatic patients, which can hinder the correct diagnosis, especially in children.

In Brazil, there is not much data available on the number of new cases in the pediatric age group. Studies in other countries estimate that the number of cases in the pediatric range is 1% to 5% of the total confirmed cases. ¹⁷ In the present study, among the 147 children suspected of having COVID-19, 20 (13.60%) presented positive results. In addition, from the total number of patients investigated in the 3 Brazilian municipalities in the border region (1874), in the period covered by the study, children aged 0 to 15 years represent only 0.56% of those infected. However, the Paraná News Agency, ¹⁸ reported that the number of infected children has been growing in the state. Data from the State Department of Health indicate that the cases in July alone were greater than the other previous months combined. This growth in confirmation among children may also be possible due to family members not adhering to social isolation since classes were suspended in schools. These data corroborate with the present research, which shows that in the months of March, April, and May, there were no reports of cases in children in the 3 municipalities of this study. June was the starting month for notifications and the 1 with the highest number of registered cases (55.00%).

Recent studies have shown that, unlike infected adults, children rarely progress to the severe form of the disease, presenting as mild or asymptomatic. ^{Reference Safadi1} Data from the Centers for Disease Control and Prevention (CDC) in the United States, ⁷ point to the fact that hospitalization for COVID-19 seems to be uncommon (between 2.50% and 4.10%), and even more rare is the need for treatment in intensive care (< 1.00%), corroborating with the data of this research, where no child needed hospitalization. According to Cunha et al., ^{Reference Cunha, Andrade, Meneguitti and Loose19} in a study conducted in Rolim de Moura, Rondônia, 5.31% of the positive cases were in children, aged between 6 months and 11 years, and all had mild symptoms of the disease and a history of family exposure. This data corroborates the present study which shows that children diagnosed with COVID-19 presented symptoms common to respiratory diseases such as fever, headache, cough, and nasal congestion, as well as sore throat, coryza, myalgia, and diarrhea. Other symptoms included weakness, dyspnea, and vomiting. It is known that 65.00% of the children were infected through exposure to family contacts.

A study by Lu et al. ^{Reference Lu, Zhang and Du20} in Wuhan, China, observed 171 children infected with SARS-CoV-2, from 1 day to 15 years old. Among the symptoms, the most frequently observed were cough (present in 48.50% of cases), followed by pharyngeal erythema (46.20%), and fever (41.50%), corroborating the data found in this research, which showed that the most frequent symptoms in children were fever, present in 65.00% of cases, followed by headache (60.00%), cough (55.00%), nasal congestion, and sore throat, both found in 35.00% of cases.

A study conducted in China by Liu et al. ^{Reference Liu, Zhang and Chen21} observed 59 patients; among these, 4 (6.77%) were children with a positive diagnosis of COVID-19 (2 males, 50.00% and 2 females, 50.00%). All of them had been exposed to confirmed or suspected patients with COVID-19. Hoang et al. ^{Reference Hoang, Chorath and Moreira22} found in the systematic literature review a slight predominance of males (55.00%) and a history of symptomatic household contact in 75.00% of cases of children with a positive diagnosis for COVID-19.

Another team from São Paulo, in July 2020, with 66 patients diagnosed with COVID-19 by RT-PCR, and with an average age of 7 years old, revealed data similar to those described in this research: a predominance of males with 41.00% of them having a history of contact with patients who had some type of respiratory symptom. ^{Reference Vieira, de Aguiar, Verlangieri, de Araujo Evangelista, Otsuka and Sarrubbo23} The Paraná News Agency, ¹⁸ shows that 2908 cases of children infected with the new coronavirus were reported in the state from March to June, 2020, also with a predominance in males (54.36%). These data corroborate with the present research, as it was possible to identify that of the 20 children diagnosed with the new coronavirus, 60.00% were male and 40.00% female. Besides, among these, 13 (65.00%) were exposed to confirmed patients within their own family circle.

According to the epidemiological data described in different studies, most children with COVID-19 are asymptomatic or have mild symptoms of the infection. However, studies point to some cases of children who developed a significant systemic inflammatory response. ^{Reference Yonker, Shen and Kinane24} In late April 2020, doctors in the United Kingdom recognized a significant increase in children who had an inflammatory syndrome, associated with the cases of COVID-19. This syndrome is currently referred to as the Multisystem Inflammatory Syndrome in Children (MIS-C). ^{25–Reference Jones, Mills and Suarez27} This syndrome describes a new health condition seen in children who were infected with new coronaviruses, recovered, and later show an immune response that results in significant levels of inflammation in the organ systems. ²⁵

The clinical manifestations of MIS-C are similar to other inflammatory entities such as Kawasaki disease, toxic shock by staphylococci and streptococci, bacterial sepsis, and secondary hemophagocytic lymphohistiocytosis (HLH) syndrome, as well as macrophage activation syndrome (MAS). ²⁵ WHO has made available an online worldwide registry so that pediatric doctors from all over the world can enter data on suspected cases, in order to be able to investigate the real incidence of MIS-C and its relationship with COVID-19. ¹⁷ There is a certain disagreement about the time of immunological window for the development of the syndrome. However, it is accepted that children (with a recent infection or who had a previous history of the diagnosis of COVID-19) developed the syndrome. ^{Reference Uchiya28} In Brazil, until the end of August 2020, the Ministry of Health reported the occurrence of MIS-C temporarily associated with COVID-19 in 197 children and adolescents from 0 to 19 years old, with 14 deaths. In Paraná, according to data from the State Department of Health, until the end of August, 10 cases were reported in children and adolescents between 3 and 16 years old, with 3 deaths. ²⁹ The non-occurrence of MIS-C in the municipalities chosen for this study does not exclude the possibility of the existence of this syndrome in the region, since under-reporting or non-identification of the syndrome may occur.

Another important fact to be considered is that coronaviruses (CoVs) can be found in different hosts and circulate in the wild in different animal species. Considering the animal origin of SARS-CoV-2, it is likely that its relevance does not occur only in infections in humans and may develop into a zoonotic disease. ²⁹ The literature is still scarce, but it indicates that some animal species, felids in particular, may occasionally become infected with SARS-CoV-2. ^{Reference Shi, Wen and Zhong30,31} According to World Organization for Animal Health (WOAH), ³² some dogs and cats tested positive for the new coronavirus due to close contact with infected people. Although the results found in literature show an infection, mainly of felines, by COVID-19, and a possible human - animal transmission, there are still no scientific revelations that indicate the transmission of SARS-CoV-2 from domestic animals to humans.

The World Small Animal Veterinary Association (WSAVA), the WOAH, and the Centers for Disease Control and Prevention (CDC), ^31–33 recommend that people who tested positive for COVID-19, and who own pets, should limit contact with their animals, the same way they do with humans, for up to 14 days. These questions about the possibility of human - animal and animal transmission serving as carriers of the virus to other animals or humans make surveillance of this disease even more important, especially considering the relationship between children and family pets.

The proximity of the municipalities considered in this study to the border region between Paraguay and Argentina further aggravates the key to viral transmission since it is known that SARS-CoV-2 entered Brazil through airports, installed itself in cities with a greater connection to foreign countries, and quickly penetrated the territory. ³⁴ Also, the border region facilitates the transit of people, goods, and animals between countries, enabling a viral spread that is difficult to control, especially when it comes to smuggling, a situation easily found in these regions. ^{Reference Amaral35,Reference Barbosa36}