The COVID-19 Epidemic:
The mean (SD) number of articles per week for the control period (from 6th January to 8th December) was 9.8 (2.9), and this level was considered as the baseline. After the epidemic start-time on 8th December 2019 (1,16), the first week that showed a significant increase in the number of articles than the baseline was 19-25th December (documents number =21, p< 0.001) and, such increase was repeated in the next weeks (Figure 1). Notably, 29th December to 4th January also showed a significant increase in the number of articles (documents number= 17, p< 0.01); however, this result was not repeated in the next two weeks, and we did not consider this record as a significant increase. Therefore, the time range between rising in the number of articles and the epidemic start-time was six weeks and, the time range between this rising and notifying to WHO of the epidemic (31st December 2019 (22)) was three weeks.
The three most frequent MeSH subheadings assigned to the articles about coronaviruses indexed in 2020, up to 10th April, were etiology (340 articles), statistics & numerical data (272 articles), and epidemiology (270 articles) (Figure 2). In contrast, the three most common MeSH subheadings for articles of the year 2019 were etiology (233 articles), microbiology (171 articles), and genetics (125 articles). Statistics & numerical data, epidemiology, transmission, diagnosis, and organization & administration were five topics that their ranks in frequency were increased in 2020 than in 2019. Besides, the increase in relative frequency was significant for all these topics along with prevention and control (0.041 vs. 0.071, p-value <0.001).
The SARS Epidemic:
The mean (SD) number of articles per month added to the PubMed database in the control period (1st November 1998 to 1st November 2002) was 6.7 (3.27). We considered this number of articles per month as the baseline. In the epidemic course, which started in November 2002 (17), the first month, which showed a significant increase in the number of articles compared to the baseline, was April 2003 ( documents number= 17, p<0.001) (Figure 3). This significant increase than the baseline was also repeated in the next few months. Therefore, the rise in the number of indexed articles occurred approximately five months after the epidemic started, and two months after the epidemic was reported by WHO ( February 2003 (8)).
The three out of eleven most common MeSH terms assigned to the articles that are about coronaviruses and indexed in 2003 were as follow etiology (234 articles), microbiology (122 articles), and genetics (121 articles) (Figure 4). These three MeSH subheadings were also the most frequent ones in 2002, and the frequency was 95 articles for etiology, 62 articles for genetics, and 49 articles for microbiology. The rank of five topics in frequency was increased in 2003 than 2002 that comprises: microbiology, statistics & numerical data, epidemiology, diagnosis, and drug therapy. However, diagnosis and transmission were the topics that their relative frequency was increased significantly (0.028 vs. 0.088 for diagnosis, 0.007 vs. 0.042 for transmission, p-value <0.01).
The Ebola Epidemic:
The mean number of articles per month indexed in the control period (1st December 2009 to 1st December 2013) was 8.1 (2.62), and this level was considered as the baseline. In the epidemic course, a sustained significant increase in the documents number compared to the baseline was started from July 2014 (documents number=17, p<0.001) (Figure 5). April 2014 also showed a significant increase in the documents number than the baseline (documents number=18, p<0.001); nevertheless, this increase was not repeated in the next two months. This epidemic started in West Africa in December 2013 and was declared in March 2014 by WHO (18,23,24); therefore, the sustained rise in the number of indexed articles occurred seven months after the epidemic start-time and four months after the epidemic declare-time.
The three most frequent MeSH subheadings assigned to the articles that are about the Ebola virus disease and added to the PubMed database in 2014 were statistics and numerical data (421 articles), epidemiology (407 articles), and prevention and control (373 articles) (Figure 6). However, in 2013, the most common MeSH subheadings in the articles that are about the Ebola virus disease were etiology (72 articles), genetics (47 articles), and immunology (34 articles). The six topics that their ranks in frequency were increased comprises statistics & numerical data, epidemiology, prevention & control, organization & administration, transmission, and diagnosis. Similarly, the increase in relative frequency was significant for these topics except diagnosis (0.015 vs. 0.044, p-value= 0.012)