Talk:Origin and global diffusion of the pandemic

The COVID-19 pandemic in Spain. First wave: from the first cases to the end of June 2020

Monographs from the National Atlas of Spain. New content

Thematic structure > Global context of the COVID-19 pandemic > Origin and global diffusion of the pandemic

SARS-CoV-2 virus, known as COVID-19, was declared a health emergency towards the end of 2019 following an outbreak in the Chinese city of Wuhan. However, the results of water analyses gathered later from various parts of the world suggest it was already circulating before then. Initially, it presented as an acute health problem that spread from the original outbreak in Wuhan to other major metropolitan regions in China, particularly Shanghai, Chongqing and the Pearl River Delta (Guangzhou, Hong Kong, Shenzhen, etc.). Analyses of this expansion from data on public transport use, particularly the high-speed train –despite the small amount of data available from China–, explain the pandemic’s rapid spread throughout its vast territory. During the final months of 2019, it appeared the spread of the infection would be limited to China and to a few of its neighbouring Asian countries. However, international airports eased its spread to the rest of the world, and the World Health Organisation (WHO) declared it a global pandemic in early March 2020. The spread of the pandemic may be observed on the map on the origins and spread of COVID-19, which shows the number of cases per country and month from February to July 2020. The peak of infections was registered in early April 2020. The lack of effective treatments for severe cases and little knowledge of how COVID-19 was transmitted during that period meant that it proved to be a highly lethal disease that resulted in tens of thousands of deaths. However, the severe lockdowns applied in many countries succeeded in gradually reducing the number of deaths from that first wave.

The spatial diffusion of the pandemic across continents followed a predictable pattern. Initially, the virus spread from China to the rest of Asia. However, the strict lockdown measures adopted by some countries curbed the increase in infections there. Subsequently, the virus reached Europe, where it spread rapidly and soon reached the maximum number of infections in absolute terms. Later, COVID-19 was spread to the Americas, where it quickly spread. In fact, the Americas were the hardest hit continents, only lagging behind Europe for a few weeks. Finally, the pandemic also extended to the other continents but with a much lower incidence, as happened in Africa, for example. There is, however, a possibility that the apparent lower prevalence in Africa may owe more to a lack of effective recording and to the fact that this new virus was just one more health problem in societies that are already highly vulnerable to all kinds of infectious and contagious diseases.

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  Statistical graph: Evolución de casos COVID-19 en el mundo. 2020. Mundo.
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  Statistical graph: Evolución de fallecidos por COVID-19 en el mundo. 2020. Mundo.
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  Statistical graph: Evolución de casos COVID-19 por grandes regiones del mundo. 2020. Mundo.
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  Statistical graph: Evolución de casos COVID-19 en los países más afectados. 2020. Mundo.

Map: Origen y difusión del COVID-19 en China. 2020. China. PDF. Datos.

Map: Origen y difusión del COVID-19 . 2020. Mundo. PDF. Datos.

When analysing the spatial diffusion by country, it is helpful to differentiate the results in absolute and relative terms. On the one hand, China went from being the origin of the infection to playing a very discreet role in the global ranking. In absolute terms, the United States ranked as the world leader in terms of the total number of patients from the end of March 2020, with Brazil ranking second behind it. These two countries, with over 500 million inhabitants between them, have clearly topped all statistics in absolute terms since then. By contrast, in relative terms, Chile and the European States most impacted during the first wave, such as Belgium, Spain and Sweden, stand out for their high incidence among smaller populations. In other large countries, such as Russia and India, cases evolved in an ascending pattern before reaching a certain level of control, and they were amongst the top five countries for the total number of infections throughout the whole period under study.

Having analysed the origin and expansion of the pandemic worldwide, the following paragraphs deal with its magnitude. In this context, three key aspects shall be evaluated in order to understand the scale of the problem: the number of COVID-19 cases recorded between January and June, the number of deaths and the number of healthcare workers.

Map: Personal sanitario en el mundo. 2018. Mundo. PDF. Datos.

The number of COVID-19 cases shall also be analysed in absolute and relative terms. In absolute values, the countries with the highest number of recorded cases during the first wave of the pandemic were the United States, Brazil, India and Russia, which is consistent with their large size. However, what is striking is that some other countries with less than 70 million inhabitants also feature at the top of the list, including the United Kingdom, France, Italy, Spain, Chile, Peru and Saudi Arabia. The high number of cases in these countries could be attributed to the high demographic densities in their urban areas, which are home to a sizeable part of their population, and the lack of an effective response to the outbreak during the initial weeks of the pandemic that allowed the virus to spread. In relative terms, the countries with worst data are the United States, Panama, Brazil, Peru, Chile, Spain, Belgium, Luxembourg, Ireland, Sweden, Belarus, Armenia, Kuwait, Qatar, Oman and Saudi Arabia, some of which are also amongst those worst affected in absolute terms. It shall be noted that the governments of some countries, such as the United States, Brazil and Belarus, showed some initial scepticism toward the threat of the pandemic and failed to take decisive measures to contain the spread of the virus. The evolution of the pandemic in Sweden, for example, was probably influenced by the implementation of deliberately lax lockdown measures that sought to seek a supposed herd immunity.

At the opposite end of the scale, the countries with fewer relative cases of COVID-19 fall into one of two categories: either they applied stringent isolation measures with exemplary levels of compliance from their populations, i.e., China, South Korea, Japan, Taiwan, New Zealand and Australia, or they have poor levels of record-keeping, and COVID-19 is present alongside other infectious and contagious diseases (ebola, malaria, yellow fever, etc.), i.e. sub-Saharan Africa and some countries in South America and Asia.

Map: Casos de COVID-19 en el mundo. 2020. Mundo. PDF. Datos.

The number of deaths from COVID-19 during the first wave of the pandemic was influenced by several factors, including scant knowledge of the new virus, the shortage of medical and infection prevention equipment, the absence of specific medical treatments, etc. As a result, the mortality rate stood at 5% during the initial months but decreased from June 2020 due to improved treatments and Personal Protective Equipment (PPE) availability. Given that almost 80% of those who died worldwide were men over 70 and women over 80, the age distribution of the population was another factor to have a considerable bearing on the countrywide outcome. It is in this context that the world map of relative mortality shall be understood, in which there are five Western European countries (the United Kingdom, Italy, Spain, Belgium and Sweden) with a high mortality rate per 100,000 inhabitants due to their older age-sex pyramids and despite their solid health services, which were caught unaware during the first few months of the pandemic. At the opposite end of the scale, China (although many authors question the reliability of their data), Asia in general and Africa may be found, yet younger populations shall be borne in mind.

Map: Fallecidos por COVID-19 en el mundo. 2020. Mundo. PDF. Datos.

With regard to healthcare workers, it is important to clarify two aspects: firstly, the data compiled by the United Nations for individual countries is for different years between 2010 and 2018; secondly, only doctors and nurses have been counted as healthcare workers, excluding other job categories in the sector, such as clinical assistants, pharmacy workers, etc. The main takeaway that may be extracted from this map is the sharp contrast between north and south. The north includes Europe, North America, Oceania, some of the Latin American countries and the Arab World. Indicators in this area are high both in absolute terms and relative to population size. In addition, nurses account for a large proportion of their total number of registered healthcare workers. This situation is especially true for Norway, Sweden, Finland, Germany, Switzerland, the United States, Chile, Lithuania and Belarus (these last two countries possibly as a legacy of the Soviet model). China, India and some Latin American countries have intermediate values for the number of healthcare workers relative to population size. In the south, by contrast, sub-Saharan Africa has the lowest availability of healthcare workers, with the few exceptions to this general rule being Botswana, Zambia, Gabon and Ghana.

PANDEMIA Propagación a escala mundial y a cierta velocidad de una nueva enfermedad. Se declara cuando esta enfermedad se está extendiendo amplia y simultáneamente en múltiples áreas geográficas en todo el mundo. La declaración de la Organización Mundial de la Salud (OMS) de una nueva pandemia de coronavirus fue inevitable cuando se certificaron casos de la enfermedad en más de 100 países.

COVID O CORONAVIRUS Tipo de virus que afecta a los seres humanos y que provoca síndromes respiratorios agudos severos. Forma parte de una gran familia de virus que circulan entre las personas y algunos animales, como ciertos mamíferos. Aunque existen algunos coronavirus que no afectan a la salud de las personas, el COVID-19 ataca fundamentalmente a los pulmones y puede generar neumonías; en otros casos provoca problemas gástricos o pérdida del olfato y del gusto.

DIFUSIÓN ESPACIAL Propagación, expansión o divulgación de un fenómeno en el espacio y en el tiempo. Para que se materialice el proceso de difusión es necesaria la existencia de un foco en el que se origine, de un conjunto potencial de receptores, de canales de comunicación entre el punto emisor y los receptores, y de un período de tiempo variable en cada caso. El proceso de difusión puede ser aleatorio, en mancha de aceite o a través de formas jerárquicas, pasando por puntos nodales. Los modelos de difusión espacial se generalizaron a partir del trabajo del geógrafo sueco T Haggerstränd en 1968.

TRANSMISIÓN COMUNITARIA Existe cuando en una población o territorio determinados se generalizan los contactos sin conocer su origen. Se establece al detectarse un virus en una o varias personas, desconociéndose cómo lo contrajeron. En el caso del nuevo coronavirus, la transmisión comunitaria empezó a detectarse cuando varios positivos coincidían en el hecho de haber visitado hacía poco China u otras áreas donde el virus se estaba propagando. Este tipo de transmisión significa que el virus se ha generalizado por la comunidad sin haber sido detectado por un tiempo. Cuando existe transmisión comunitaria se estima que la expansión del virus está descontrolada.

TASA DE POSITIVIDAD Porcentaje de casos positivos de COVID-19 en relación con el total de pruebas de detección realizadas. Si el porcentaje es inferior al 5% se estima que la pandemia está en vías de control. Si, por el contrario, se supera esa cifra se estima que muchos casos de personas infectadas no se conocen, por lo que es necesario hacer cribados y existe transmisión comunitaria. En general, se considera que este indicador es más preciso que el número diario de positivos, ya que el total de PCR realizados puede variar cotidianamente y la positividad nos informa del riesgo de contagio recurriendo a un porcentaje siempre comparable, si la dinámica de realización de pruebas se rige por los mismos criterios.

INCIDENCIA Número de casos detectados de una nueva enfermedad en un periodo de tiempo determinado y en una zona o comunidad concreta. Asimismo, se podría expresar como la probabilidad de que una persona de una cierta población resulte afectada por dicha enfermedad. La tasa de incidencia representa la velocidad a la que se producen nuevos casos de la enfermedad en la población expuesta. Se calcula dividiendo los nuevos casos entre el número de habitantes. La incidencia acumulada es la proporción de personas que enferman en un tiempo determinado. También es el resultado de dividir el número de casos aparecidos entre el número de personas que están libres de la enfermedad al inicio del periodo. Normalmente se suele tener en cuenta cada 100.000 habitantes y en periodos de 7 a 14 días.

CONFINAMIENTO Aislamiento temporal y generalmente impuesto a una población, una persona o un grupo por razones de salud o de seguridad. Casi siempre es el resultado de una decisión gubernativa, que implica recluir dentro de unos límites. Se trata de una medida extraordinaria y de emergencia tomada por motivos de enfermedad o de prevención, que supone el cierre de establecimientos de ocio, turísticos, culturales y en la que se restringen los desplazamientos de la población de la zona afectada. En sus casos más extremos puede ser total, aunque lo más frecuente es que se respeten los movimientos de carácter laboral, asistencial, de emergencia o el aprovisionamiento de comida y productos farmacéuticos, en distintos grados.

INMUNIDAD Forma en la que el cuerpo se protege contra las enfermedades causadas por infecciones. Estado de resistencia general que posee una persona respecto a una enfermedad infecciosa o una toxina. Se vincula a la presencia de anticuerpos o células que desarrollan una acción específica contra el microorganismo causante de la infección. Se diferencian dos tipos de inmunidad: la inmunidad activa, que suele durar años, se adquiere naturalmente como consecuencia de una infección o artificialmente a través de una vacuna; la inmunidad pasiva, de corta duración (de algunos días a varios meses), se obtiene naturalmente por transmisión materna o artificialmente por inoculación de anticuerpos protectores específicos. También se ha generalizado la expresión inmunidad colectiva, de masa o de rebaño, cuando la proporción de población inmune es alta y el agente tiene menor probabilidad de diseminarse.

PCR Y TEST DE ANTÍGENOS Pruebas utilizadas para la detección de infecciones (PCR es una sigla en inglés que significa reacción en cadena de la polimerasa). La prueba consiste en extraer material genético de una muestra y compararlo con los genes encontrados en el SARS-CoV-2 o con otros virus. Se toma una muestra de la persona sospechosa introduciendo un hisopo (bastoncillo) por la nariz o por la boca para recogerla. Si la técnica de PCR no detecta el material genético del virus, lo más probable es que la persona no esté infectada. Por su parte, el test de antígenos consiste en introducir una molécula tóxica, que genera una reacción de anticuerpos. Si esta es del virus del COVID se puede inferir si el sujeto está infectado en ese momento.

DISTANCIAMIENTO SOCIAL Expresión referida a la imposición o recomendación del alejamiento entre personas no convivientes para evitar contagios. En realidad, debería denominarse distanciamiento físico, dado que alude a todos los individuos con los que no se comparte vivienda. Esta medida se ha convertido en la recomendación más importante para contener la propagación de un virus, especialmente cuando no existen evidencias precisas del rastreo de contacto.

Co-authorship of the text in Spanish: Agustín Gámir Orueta, Rubén C. Lois González, Ángel Miramontes Carballada y Ana Paula Santana Rodrigues. See the list of members engaged

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