Because the causes of KD are unclear, it is helpful to conduct a large-scale epidemiologic survey. It is possible to find clues about the etiology and pathogenesis of the disease [15]. The scientific literature on KD since 2000 has been revised and shows that KD has been reported for more than 60 countries since 2004. The incidence rates are highest in Japan, followed by the East Asian countries surrounding Japan such as China, Hong Kong, Taiwan, and Korea. Meanwhile, the incidence rates (or at least the diagnostic rates) are increasing in many countries [26].

The incidence of KD has been increasing in the Jilin Provence of China. Based on the 10-year surveys from 1999 to 2008 in Jilin Provence, the incidence of KD increased from 1.39 per 100,000 children to 11.07 per 100,000 children younger than 5 years from 1999 to 2008, which is much lower than the incidence reported in Japan [17]. Moreover, the incidence of KD in our study also is much lower than that in Beijing, Shanghai, Sichuan Province, Hong Kong, and Taiwan, other developed areas with large population in China [5, 10, 11, 14, 19, 25]. These data together indicate that the incidence of KD among Chinese children has been significantly lower than among Japanese children [17] if these results are truly representative.

The increasing trend also has been found in many other countries and areas such as Thailand, Korea, England, the United States, and Hawaii [6‐9, 21]. Thus, the reported incidence of KD is showing a rising trend throughout the world. However, the true incidence of KD is unknown because no definite way to diagnose KD exists. The reported incidence might be increasing because of increased awareness rather than a real increase in the disease. It is worth mentioning that the incidence of KD in Jilin Provence is similar to that in Israel [3] and Chandigarh of North India [23], which may be caused by a relatively underdeveloped economy or other social reasons in these areas.

Similar to most reports, the age distribution of patients at onset of KD in our survey predominantly involved children younger than 5 years. This age group accounted for 88.73% of the KD cases [5, 10, 14, 25]. Our results are slightly different from those reported previously in the nation but consistent with the results reported in Japan [16].The peak age of KD onset was 1 year, which is similar to the onset age in Beijing [5].

Male preponderance also was seen in our series. The male-to-female ratio was 1.96:1, which is slightly higher than previously reported for most provinces in our country [5, 10, 14, 25].

According to our data, the disease occurred throughout the year, as expressed by a double-peak curve. It occurred more frequently from May to July and November and the least often in February. However, the seasonal distribution of KD occurrence varied from country to country and even from region to region. The onset of KD occurred more frequently in the summer and spring in Shanghai, Beijing, and Hong Kong [5, 10, 19, 25]. The patient numbers peaked from March to May, and the fewest KD cases occurred during September in the Sichuan province of China [14]. In Taiwan, KD occurred most frequently in the summer and least frequently in the winter [11]. Although the number was highest during the winter months, smaller increases also occurred during the summer months in Japan [17].

In the United States, the number of KD patients was highest in the winter [4]. In Korea, the highest incidence of KD was seen in June, followed by July and May, similar to our first peak [20]. The reasons for the seasonal discrepancy still remain unclear. We speculate that it may be related to climatic conditions, geographic environment, living habits, and the like.

The sequence of main clinical manifestations of KD in Jilin province was similar to that in previous national reports [5, 10, 11, 14, 19, 25]. Fever persisting 5 days or longer was the most frequent clinical manifestation of KD, followed by changes in the lips and the oral cavity, changes in peripheral extremities, bilateral conjunctival congestion, rashes, and acute nonpurulent cervical lymphadenopathy. Although not included in the diagnostic criteria of KD, perianal desquamation was seen in 32.9% of the cases as well as erythema at the Calmette-Guérin Bacillus inoculation site (1.7%).

As a systemic vasculitis, KD affects multiple systems. The respiratory system is the most commonly involved system, followed by the digestive system. Involvement can be seen in hematologic system, the urinary system, joints of extremities, and so forth. We found the peak time until medical attention to be 7.58 ± 4.63 days. Within 6 days, the patients with a KD diagnosis were fewer because early atypical clinical manifestations of KD sometimes lead to late medical attention as well as delayed diagnosis and treatment. Pediatricians should remain cautious in cases with fever that persists for 5 days or longer.

Coronary artery lesion is of great concern in KD. The CAL occurrence rate varies in different reports. In our survey, CAL was detected in 63.3% of 553 cases (49.5% with ectasia, 13.4% with stenosis, 0.36% with aneurysm) during the acute stage. The rate was greater than in other reports [2, 4, 5, 10, 11, 14, 19, 25]. The higher incidence rate might be due to progress in diagnosing KD, identifying cardiac lesions, and universally applying echocardiography. Fortunately, the proportion of patients with cardiac sequelae has decreased year by year [17]. This improvement might have been caused by IVIG therapy. It was similar to that reported previously for major cardiovascular complications, with no deaths recorded during the acute stage in China [5, 10, 11, 14, 19, 25].

Regarding risk factors of CAL in the patients with KD, this survey found that age and lower serum albumin were the most important risk factors of CAL in KD: the younger the age at onset, the higher the risk of CAL and the higher the incidence of cardiac sequelae. Probably because of delay in diagnosis, only 41% of infants younger than 6 months were treated with IVIG. Only 14% of these infants received the therapy during the first 10 days of the disease [22]. Delayed treatment also may have contributed to the development of cardiac sequelae.

Although an early study by Kato et al. [12] suggested that steroids exert a detrimental effect when used as the initial therapy for KD, subsequent studies have shown either no negative effects or a possible benefit. Arguments still exist for the use of steroids. Recent reports by Ganesh et al. [1] have suggested that corticosteroids used in regimens for the initial treatment of KD decreased rates of retreatment with IVIG. However the addition of corticosteroids to standard therapy did not decrease the incidence of coronary artery aneurysms or adverse events. Tohru et al. [13] reported that prednisolone with IVIG treatment was associated with improvement in clinical and coronary outcomes for patients at high risk for being IVIG nonresponders. In other words, steroids with IVIG in the primary therapy for KD can relieve symptoms quickly and reduce the re-application of IVIG but not the probability of CAL occurrence. It is worth noting that the patients in our data who received steroid treatment more frequently had CAL. It is possible that the severely affected children were treated more readily with steroids, reflecting disease intensity and not some direct effect of steroids themselves on the development of CAL. Nevertheless, the possible effects of steroids themselves on the development of CAL should be not ignored. Careful consideration is required before steroids are used. The use of steroids should possibly be considered only for IVIG nonresponders.

In 1991, Newburger et al. [18] reported that the regimen with 2,000 mg/kg IVIG was better than the divided dose. Terai and Shulman [24] also reported that the incidence of coronary artery aneurysm was negatively correlated with the IVIG dose: the greater the dose of IVIG, the lower the incidence of CAL. Consequently, IVIG is used more with the regimen of 1,000 mg/kg once or 1,000 mg/kg twice in current clinical practice. The reduction in CAL is partly due to this change. In the survey, for 88.7% of the patients treated with IVIG therapy, the common dose was 400 mg/kg for 5 days (39.9%) or 1,000 mg/kg twice (25.7%). Significant differences were proved between the KD groups with and without administration of IVIG, and CAL was less frequently seen in patients treated with IVIG. Simultaneously, the findings show a significant tendency for an increase in the regimen of 1,000 mg /kg twice since 2003.

The survey had some limitations. Due to the retrospective nature of the study and the reliance on data from many different centers, with each center using anticoagulant drugs different from standard therapy (intravenous immunoglobulin + aspirin) for patients with acute-phase KD, the treatment effect from every regimen of IVIG could not be proved. The optimal administrative time and dosage of IVIG deserve more observations.

In conclusion, the number of KD patients and the KD incidence rate are increasing year by year in Jilin Provence. The age and gender distributions are similar to previously reported data. Seasonal distribution differs from that of other reports, and onset of KD occurs more frequently from May to July and November. Age and lower serum albumin are the most important risk factors of CAL in KD. It is possible that patients treated with steroids are more susceptible to CAL.