Excretion of enterovirus 71 in persons infected with hand, foot and mouth disease

Hand, Foot and Mouth disease (HFMD) is a common infectious illness. It is primarily a disease among children but occasionally, it can be seen in immunocompromised or immunocompetent adults [1‐3]. This disease can be found all over the world. A number of enteroviruses can cause this disease. Enterovirus 71 (EV71) and Coxsackievirus A16 (CoxA16) are the two major pathogens for HFMD [4, 5]. Most severe cases are associated with EV71 [6‐8]. Many sporadic cases and outbreaks of this disease caused by EV71 have been reported [9‐12]. With the increasing severity and frequency of the outbreak such as Taiwan in 1998 [11, 13], Shandong province of China in 2007 [14], HFMD outbreaks have increasingly become the focus of public health issues. In order to prevent and control this disease, HFMD surveillance was brought into the observation system of contagious disease of Beijing since 2007. A series of measures have been implemented to prevent and control the spread of this disease. Since the disease is infectious and can induce severe neurological complications even death, the duration of the EV71 shedding in throats or feces of HFMD patients may have extensive implications on designing effective protective measures. Prolonged excretion of EV71 may extend the contagious period and raise the likelihood of secondary infections.

The aim of this study is to determine the duration of EV71 excretion in the throats and feces of HFMD patients and obtain more information of whether the duration of EV71 shedding was correlated with the factors of the case.

A total of 30 cases which includes 27 children and 3 adults aged from 1 to 40-year-old were enrolled in this study and were categorized into 3 groups, i.e., close contact group, mild case group, severe case group. All the specimens collected from cases and the close contacts were analyzed with real-time RT-PCR for three times and the result was the same. All the participants were EV71 positive by real-time RT-PCR. The close contacts, mild cases and the severe cases had the duration of shedding longer than 6 days, 30 days and 54 days, respectively. The severe case that shedding virus for at least 54 days failed showing up in the follow-up study for 27 days. On the 81st day the fecal sample from him was identified and the result was negative. The only one adult severe case excreted EV71 for at least 40 days. The close contact group, mild case group and severe case group turned EV71 negative with the median shedding duration of 2 days, 18 days and 25 days respectively.

Kruskal-Wallis Test was employed to compare the difference in duration of viral RNA shedding among three groups. The results showed that significant difference in duration of EV71 shedding was found among three groups (P < 0.01) (Table 1).

In order to analyze the data of EV71 excretion of all the paediatric cases, the EV71 excretion of 3 groups was compared. The participants were defined as EV71 positive if the throat swab or the fecal sample was identified as EV71 positive. As showed in Figure 1, 100% severe cases were EV71 positive during the first 15 days after the onset of the disease. The positive rate decreased gradually from the 20th days. EV71 of 61.54% severe cases turned negative during the 15–35 day. The positive rate dropped to 7.69% in the 54th day after onset of the disease. All the mild cases were EV71 positive in the first week, then positive rate declined dramatically, and 87.5% mild cases turned negative during the 10-30 days. Results of close contacts were also analyzed, and they did not excrete EV71 for a long period. All the close contacts were EV71 positive at the beginning of the epidemic. The result showed that 85.7% close contacts were detected EV71 positive only once and all the close contacts turned negative in the first two weeks after the outbreak of the epidemic.

EV71 shedding of fecal samples and throat swabs from adult participants was also analyzed (Table 2). All of the specimens collected from adult close contacts turned negative in the first two weeks of the epidemic. The only one adult severe case excreted EV71 for at least 40 days.

Results of fecal samples and swab samples showed that EV71 was excreted intermittently in severe cases and mild cases. 66.7% severe cases and 50% mild cases showed the phenomena of excreting EV71 intermittently both in the throat swabs and in the feces samples. A positive correlation was not found between the fecal samples and throat swabs. Fecal samples and throat samples from 2 close contacts were collected. Two days later, both of them showed the symptom of HFMD. Based on their symptoms, they are classified as mild case. Throat samples from both them were EV71 positive. Fecal sample from one case showed EV71 positive.

It was reported that most children experiencing infection of EV71 will cease shedding virus particles within 13 to 24 days after the disease onset [15]. The longest EV71-positive time in throat swab was reported 24 days and in feces 42 days after onset [15]. However no one reported how long the severe cases, mild cases, close contacts shed virus. This study examined the duration of EV71 excretion in sequential fecal specimens and throat swabs from mild cases, severe cases and close contacts which were definitely EV71 positive.

Using the data of this study and the Kruskal-Wallis Test, the results showed that significant difference of the duration of EV71 shedding was found among severe cases, mild cases and close contacts. This phenomenon is different from some other virus such as HAV, rotavirus, the excretion of which does not show any correlation with the severity of the disease [16, 17]. Whether or not the duration of HAV excretion is correlated with the age of the patients has been reported previously [16, 18]. However, the obtained results were different. Since the sample size was small, our data did not provide the information of whether the factors of age and sex influence the duration of the virus shedding. The reasons why the EV71 shedding was different among severe cases, mild cases and close contacts remain to be elucidated.

This study showed that the longest duration of EV71 shedding in fecal sample is 54 days and 30 days in throat swabs. Some researchers have reported that enterovirus shedding in fecal samples lasts for a longer period than in throat swabs [15, 19, 20]. EV71 is transmitted predominantly via the faeco-oral route. Prolonged excretion of EV71 will act as an on-going infection source which will play an important role in outbreaks of HFMD. This study showed that some individuals shed other enterovirus in the fecal samples after EV71 could not be detected. In this study we also found that EV71, just like rotavirus [17] or poliovirus [21], has a phenomenon of excreting virus intermittently both in fecal samples and in throat swabs after apparent recovery from initial infection. Children or adults excreting EV71 intermittently for a long time may serve as reservoirs of the virus and thus contribute to the epidemic of the HFMD.

The findings in our study suggest that patients may excrete EV71 for a long period. It means that the majority of severe cases may still be infectious during their recovery even though they are asymptomatic. The role of these prolonged excretion in perpetuating epidemics of HFMD is uncertain. In order to thoroughly eliminate the potential infective sources from the community, one solution might be for cases to be separated from other susceptible children until patients no longer excreting virus, especially for severe cases. In this study we also found that some cases were EV71 positive before they showed the typical HFMD symptoms. This phenomenon implied that cases began to excrete EV71 just at the latent period. It was a blind spot for disease prevention. So we suggest that it is necessary to make preventive measures such as sanitation, disinfection and hand-washing, especially among people at risk such as children under the age of five years old. Timely preventive measures will limit secondary cases of HFMD.