A Case-control Study on Risk Factors for Severe Hand, Foot and Mouth Disease

The objective of this study was to identify potential risk factors for severe hand, foot and mouth disease (HFMD). In this case-control study, 459 severe HFMD patients and 246 mild HFMD patients from Guangdong province and Henan province, China were included. Data comprising demographic characteristics, clinical symptoms and signs, laboratory findings and other factors were collected. Univariate analysis revealed 30 factors associated with severe cases. Further multivariate analysis indicated four independent risk factors: fatigue (p < 0.01, odd ratio [OR] = 204.7), the use of glucocorticoids (p = 0.03, OR = 10.44), the use of dehydrant drugs (p < 0.01, OR = 73.7) and maculopapular rash (p < 0.01, OR = 84.4); and one independent protective factor: herpes or ulcers in mouth (p = 0.01, OR = 0.02). However, more systematic research and validation are needed to understand the underlying risk factors for severe HFMD.


Results
General characteristics of the participants. In total, 705 cases of HFMD were recruited, comprising 459 severe HFMD cases and 246 mild HFMD cases. The overall median age of the participants was 23.7 months (range 0-131 month) and the gender ratio was 1.9:1 (male: female). Table 1 outlines the demographic characteristics of all subjects including gender distribution, age distribution, the proportion of floating population and permanent resident population. Severe cases tended to be coming from the floating population and a significant difference was observed with respect to of position of residence. The general characteristics of cases and controls are summarized in Table 2. It shows that cases had significant higher birth weight, less breast-feeding, more allergic history and longer time interval between symptoms onset to being hospitalized. Besides, there were no statistical differences in the respect of other demographic and general characteristics among case and control groups.   Univariate analysis. Clinical symptoms and signs, drugs use methods and laboratory findings of cases and controls are presented in Tables 3, 4 and 5. For clinical symptoms and signs, severe cases had a higher incidence of fever (≥ 37.3 °C), fatigue, limb trembling, dyspnea and vomiting, but a lower incidence of startle (move or jump suddenly in surprise or frighten). While the highest level of fever, twitch (sudden muscle spasm) and runny nose did not differ between severe cases and controls. Significant differences were also observed in the rash morphology and the position of their appearance. For severe cases, maculae and maculopapules were more frequently observed than herpes, but there was no difference with papule between case and control groups. Moreover, severe cases tend to have more rashes on the hips, ulcers on the cheeks, while having fewer ulcers in the mouth, rash on limbs, and ulcers on lips. Results from performed laboratory tests were analysed from both case and control groups (Table 4). Comparing with controls, cases tend to have higher white blood cell (WBC) count and neutrophilic granulocyte (NEUT) percentage but lower lymphocytes (LYM) percentage. The therapeutic interventions given to participants from onset of HFMD until onset of severe complications were also obtained and summarized into five categories (Table 5). Cases and controls showed a significant difference with respects to all five therapeutic categories. Severe cases were more likely to use febrifuge (79.0% vs. 12.2%), glucocorticoid (92.4% vs. 15.9%), antivirotic (98.0% vs. 78.1%) and dehydrant drugs (87.2% vs. 2.9%), while non-severe cases had higher proportion using antibiotics (92.1% vs. 96.6%).

Multivariate analysis.
To determine the relative importance of the various factors associated with severe HFMD, we further performed a multivariate analysis. In the logistic regression model, maculopapular rashes, fatigue, the use of glucocorticoid and dehydrant drugs were significantly associated with increased risk of severe HFMD, with odd ratios (ORs) of 84.4, 204.7, 10.44, 73.7, respectively. On the other hand, herpes or ulcers in the mouth (OR = 0.02) was significantly associated with protections against severity ( Table 6).

Discussion
Although the majority of HFMD cases are generally mild and self-limiting, a small proportion of patients may rapidly develop severe complications which could be life-threatening 15 . Previous studies have shown that close monitoring and stage-based management program speculated with earlier admission of high risk groups, usage of IVIG, more advanced intensive care management may significantly decreased the case fatality rate 16 . Therefore, it is necessary to identify the risk factors, which may predict the occurrence of severe cases. This study aims to explore the risk factors that might indicate a child's risk of progression to severe HFMD and to provide further information to help identify patients who may progress at an early stage.
In this study, risk factors for severe HFMD were fatigue, maculopapular rash, absent ulcers in the mouth and lower platelet count, the use of glucocorticoid and dehydrant drugs. It is also shown that demographic and general characteristics of patients did not affect the disease severity. Fatigue could be a marker for central nervous system involvement. According to the epidemic of EV-A71 in Taiwan in 1998, central nervous system involvement first developed in the most severe cases, followed by circulatory system involvement 17,18 . In the most severe cases, patients developed tachycardia and cyanosis within 2 to 5 days after onset of HFMD, and died within 12 to 18 hours after onset of these symptoms 19,20 . Therefore, children with fatigue should be early recognized and monitored closely in order to prevent fatal complications. Rash morphology and its position would also predict a more complicated or fatal HFMD. We found that the absence ulcers or herpes in the mouth and the presence of maculopapular rash were indicators of severe disease, which is consistent with previous studies 15,21,22 . However, in a recent meta-analysis 23 , different findings were presented, showing that there may be no association between ulcers in the mouth and the risk of progressing severe complications. Platelet count increase associating with severe HFMD was reported in some studies. In contrast, we found that comparing with severe cases, the platelet count of non-severe cases was significantly higher, while more of severe cases (53.82%) had normal platelet count.
We also found that the use of glucocorticoids and dehydrating drugs, which were used to ease up body's response to inflammation and attenuate encephalic hypertension of the central nervous system of severe cases, was associated with an increased risk of severe HFMD. Our study results reinforce the previous findings that early use of glucocorticoids may increase the risk of subsequent severe or fatal HFMD 21,22 . It has been reported that early use of glucocorticoids was associated with critical complications of HFMD within the first 48 hours of onset 24 . Glucocorticoids may impair innate immunity by inhibiting the activity of the innate immune system and suppressing the secretion of diverse immune mediators 25 . Animal studies were also conducted, showing that mice given dexamethasone after exposure to EV-A71 develop substantially higher viral loads and virus was found in the brain 26 . Therefore, we suggest that administration of glucocorticoids for early treatment of HFMD may account for the development of critical complications. There is no further evidence that using dehydrating drug would increase the risk of developing severe HFMD.
Among twelve demographic and general characteristics, floating population, birth weight, breast-feeding, allergic history, and time interval between symptoms onset to being hospitalized were associated with severe involvement in the univariate analysis, but lost statistical significance in the final model. Besides, there were no statistical differences in the respect of other demographic and general characteristics among case and control group. Therefore, we assumed that population pattern may not influence the severity of the disease, which was consisted with some previous findings.
Besides, there are a few limitations in this study should be considered. Because of the limited sample size of the control group, the study did not use a matched method. In logistic regression model, 95% confidence intervals for each variable are large due to the deletion of miss values. There was no viral diagnostics included, which could not identify virus genotyping. Since the study is hospital-based, the sample source of our research is limited and may cause selection biases. As a retrospective case-control study, the recall bias may be a concern. However, to reduce recall bias, in this study, the data were mainly collected through medical record, while face-to-face interviews with children's parents were adopted only when study-related information was missing in medical records. In conclusion, our findings suggested that clinicians should be cautious if children are diagnosed with HFMD with maculopapules but without herpes or ulcers in the mouth and showing fatigue. Besides, the use of glucocorticoid in the early stage of the disease should be conservatively due to its potential harmful impact.

Methods
Study design and case definition. The study was designed as a retrospective non-matched case-control study. Clinical data from HFMD cases who were admitted between January 2010 and December 2014 were retrospectively collected from the Infectious Diseases Surveillance System of Henan Province and the Yuebei People Hospital in Guangdong in 2015. Face-to-face interviews with the patient's parents or guardians were held during the patients' hospitalization time. Children (under 14 years old) were diagnosed HFMD if they had at least one of the following features: maculopapular or vesicular rashes on the palms and/or soles and vesicles or ulcers       Table 6. Multivariate analysis on risk factors for severe hand-foot-mouth disease among children. Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 '.' .