Analysis of seasonal tendencies in pediatric Henoch–Schönlein purpura and comparison with outbreak of infectious diseases

Hwang, Hyun Ho; Lim, In Seok; Choi, Byung-Sun; Yi, Dae Yong

The relationship between the incidence of HSP and predisposing diseases has been investigated in previous studies. Although various causes have been reported, it is known to occur mainly after respiratory infections such as those caused by streptococci, staphylococci, and mycoplasma. [2, 17] There are reports of preceding gastrointestinal tract infections caused by Helicobacter pylori or Campylobacter. [5, 18, 19] Nevertheless, the etiology of HSP often remains unknown. Almost 70% of the cases of HSP in children reported in Spain occurred in fall and winter. [20] This higher incidence in the coldest months further supported an infectious trigger in the pathogenesis of the disease. Moreover, in this population study, upper respiratory infections were described as the potential precipitating event in more than 30% of the cases. By contrast, in the same region of NW Spain, adults in whom HSP occurred in summer were more susceptible to develop permanent renal involvement. [21] However, studies on viral infections as the leading cause of HSP have limitations. HSP was reported in the 2009 influenza virus pandemic, and there have been reports that HSP incidences followed influenza vaccinations. [22] [23] [24] However, most of these studies are case studies or cross-sectional studies from several institutions, and no large-scale studies have been conducted using the database of an entire country's healthcare system. In addition, different types of viral infections prevail in different regions, and their timings could vary. For this reason, our findings are important and meaningful because this is the first study to investigate the relationship between HSP and the preceding infectious diseases Table 2 Analysis of monthly, seasonal, and yearly incidences of newly diagnosed Henoch-Schönlein purpura according to age groups. Though HSP was known to affect boys predominantly, in our study, it was found to occur more in girls in South Korea. [2, 6, 25] Previous studies have reported that HSP is commonly seen in winter or from late autumn to early spring, and we have confirmed a similar pattern. [2, 6, 26] We found that it predominantly occurred in spring and specifically in March, and less in the summer particularly in August, although the number of cases reported in August was never <5.7% of that reported for the whole year. Of all the HSP patients in this study, 17.6% were hospitalized, and 15 of them were operated on. However, since only the patients who were first diagnosed with HSP between January 2013 and December 2016 were included in the study, we could only identify those who were hospitalized at the time of the first diagnosis. Patients who visited the hospital for the first time and did not get hospitalized, but were later admitted or operated due to severe symptoms, were excluded from the study. Therefore, the proportion of the inpatients and the number of surgical patients are expected to be slightly higher than found in our results Based on our results, some of the known infectious causes of HSP were identified. Previously known infectious agents, such as adenovirus, were associated with HSP and were found to be statistically significant even in our study using national health data. [2, 26] However, adenovirus did not show any significant seasonal tendency and was found to occur evenly throughout the year. Several studies have described the influenza virus to be a predisposing cause of HSP with significant association with HSP incidences