Introduction

Novel avian-origin influenza A(H7N9) virus was identified in March 2013 in China, and continue to cause human infections [1]. As of March 18, 2014, a total of 385 laboratory-confirmed human cases with avian influenza A(H7N9) virus infection were reported in Mainland China, and around 12% of them were from Jiangsu Province located in the eastern China (from China Information System for Disease Control and Prevention, http://10.249.1.170/). The first case as well as most of the cases reported in 2013 came from Yangtze River Delta Region, which consists of Jiangsu Province, Zhejiang Province and Shanghai Municipality[2]. Most of the H7N9 patients were severely ill; of them, 76.6% were admitted to an intensive care unit (ICU) [3]. To date, there is no evidence of sustained human-to-human transmission. In contrast, the clinical severity of pandemic A(H1N1) 2009 (H1N1pdm), a swine-origin reassortant virus which is able to transmit efficiently among individuals, were much milder with a case-ICU rate of 7.9–75 cases per 100,000 infections [4]. Even though, a large quantity of severe H1N1pdm patients was reported due to the widespread transmission of virus in human population. Owing to improve our understanding regarding the distinguishing clinical features of severe patients caused by these two viruses, we aimed to compare the key variables of laboratory-confirmed human cases of influenza H7N9 and H1N1pdm in Jiangsu Province of China.

Materials and Methods

Results

The median age of severe H7N9 patients was significantly older than that of severe H1N1pdm patients (59.0 vs.27.0 years, P < 0.0001). Patients older than 70 years accounted for a proportion of 35.1% for H7N9 but only of 5.4% for H1N1pdm (Fig. 1). Male accounted for a proportion of 73.0% in severe H7N9 patients whereas only 48.4% in severe H1N1pdm patients. No significant difference in BMI was observed between those two groups of patients (median, 23.9 vs. 22.9, P = 0.084). Severe H7N9 patients were more likely to have at least one chronic medical disorder (55.6%) than severe H1N1pdm patients (34.5%) (P = 0.018). Cardiovascular disorders (excluding hypertension) were most frequently reported (25.0%) in severe H7N9 patients but not in severe H1N1pdm patients (7.3%) (P = 0.004). Pulmonary disorders (including asthma), metabolic disorders (including diabetes mellitus) and other chronic disorders were also reported more frequently in severe H7N9 patients than in severe H1N1pdm patients, however, without any statistically significant differences. The pharmaceutical interventions in both types of cases were observed to be similar. Most of the patients of both H7N9 and H1N1pdm were treated with neuraminidase inhibitors, antibiotics and glucocorticoid, however, the clinical outcome was quite different. Nearly 85% of severe H7N9 patients were admitted to intensive care unit (ICU) compared with a proportion of 65.2% in severe H1N1pdm patients (P = 0.026). Complications including acute respiratory distress syndrome (ARDS), respiratory failure, liver and renal dysfunction occurred more frequently in severe H7N9 patients, resulting in a significantly higher fatality rate than in severe H1N1pdm patients (45.7% vs. 15.3%, P < 0.0001). The most common complications were ARDS and respiratory failure in both H7N9 and H1N1pdm patients. The time intervals (days) from the onset of illness to first medical consultation, to hospitalization, to neuraminidase inhibitors administration and to death were significantly longer in severe H7N9 patients (Table 1).

Download:

• PPT
  PowerPoint slide
• PNG
  larger image
• TIFF
  original image

Fig 1. Age distribution of severe patients infected with influenza H7N9 and H1N1pdm in Jiangsu Province, China.

https://doi.org/10.1371/journal.pone.0120999.g001

Download:

• PPT
  PowerPoint slide
• PNG
  larger image
• TIFF
  original image

Table 1. Distribution of selected variables between severe H7N9 and H1N1pdm patients.

https://doi.org/10.1371/journal.pone.0120999.t001

Interestingly, after adjusting age and gender, no difference in chronic medical conditions remained significant between severe H7N9 and H1N1pdm patients. In the context of clinical outcome, ICU admission and respiratory failure became insignificant while ARDS, liver and renal dysfunction, and death remained significant between the severe H7N9 and H1N1pdm patients. In addition, only intervals from the onset of illness to neuraminidase inhibitor treatment and to death were still significantly longer in severe H7N9 patients than severe pH1N1 patients after adjusting age and gender (Table 1).

Discussion

Most of the H7N9 patients were older male while most of the H1N1pdm patients were young without significant difference in gender [3, 8]. Significant differences were observed in age and gender between severe H7N9 and H1N1pdm patients in this study, which were consistent with another study conducted in patients hospitalized with H7N9 and H1N1pdm in China [9]. Chronic medical conditions are considered to be associated with the risk of hospitalization and prognosis of the patients infected with influenza virus [9], which need to be paid close attention by health care providers in prevention and treatment. Severe H7N9 patients were found more likely to have chronic medical conditions than severe H1N1pdm patients in gross comparison both in this study and a previously conducted study [9], however, the differences became insignificant after adjusting age and gender. This finding suggests that the differences in chronic medical conditions were probably due to the different demographic characteristics rather than susceptibility to severe infections with different influenza subtypes. No differences were found in treatment between H7N9 and H1N1pdm either before or after adjusting age and gender, which suggested that the combination of neuraminidase inhibitor, antibiotics and glucocorticoid was commonly applied for treating severe infections with both influenza subtypes, probably because of the high incidence of bacterial co-infection and its poor prognosis [10, 11].

Although the definitions of severe cases with H7N9 and H1N1pdm were comparable, a significantly worse clinical outcome was observed in H7N9 patients regardless of age and gender. Complications such as ARDS, liver and renal dysfunctions were much more frequent in severe H7N9 patients leading to a 3-fold case-fatality rate than severe H1N1pdm patients. These complications should be noticed to the clinicians owing to improve the clinical outcomes of H7N9 patients.

Time interval from onset of illness to first medical consultation was associated with severity of influenza infection [12]. Patients’ ages and influenza subtypes could influence the time intervals [13]. This might be the reason why the difference in time interval of medical consultation became insignificant after adjusting age and gender in our study. It seems that the two influenza virus subtypes has no obvious influence on infected patients’ medical consultation behaviors. The interval from onset of illness to neuraminidase inhibitor treatment was found significantly longer in severe H7N9 patients regardless of age and gender. Neuraminidase inhibitors treatment were commonly applied clinically during the H1N1pdm-driven pandemic period but has not been recommended to be widely used for outpatients with influenza like illness (ILI) in China. Thus, most H7N9 patients received neuraminidase inhibitors treatment when confirmed to be H7N9 cases or considered to be probable H7N9 cases, which led to a significantly longer interval from illness onset to anti-influenza medication.

Wang C et al found that the median time from onset to death was 18 days and 15 days for hospitalized H7N9 and H1N1pdm patients, respectively [9]. In our study, the time intervals were 24.5 days and 13.0 days for severe H7N9 patients and H1N1pdm patients. The differences between studies might be due to the various medical levels related to the geographic locations of the study populations. The interval from onset of illness to death was significantly longer in severe H7N9 patients even after adjusting age and gender, which suggested that the disease course of severe infections with H7N9 and H1N1pdm was different.

Although all the eligible cases in Jiangsu Province of China during the study period were included in this study, the sample size was small, which limited the statistical power. However, an average power of 0.765 (range, 0.279–1.000) was achieved, which was computed by Power Analysis & Sample Size software (PASS, http://www.ncss.com/software/pass/) using the observed values of each selected variable in this study (excluding variables regarding treatment and other disorders in chronic medical conditions, because their differences between groups were no more than 0.015). In fact, the statistical power was more than 0.80 and 0.60 in comparisons of 55.6% and 83.3% of selected variables, respectively (Table A in S1 File).

It has been reported that age and gender are associated with patients’ chronic medical conditions and clinical outcomes [14, 15]. Our results suggests that age and gender should be adjusted as important confounding factors when comparing the clinical features between severe H7N9 and H1N1pdm patients to avoid any misunderstanding regarding the differences between these two diseases particularly in terms of clinical severity and prognosis.

Supporting Information