Middle East respiratory syndrome coronavirus disease is rare in children: An update from Saudi Arabia

Abstract

Core tip: The number of the pediatric Middle East respiratory syndrome-coronavirus (MERS-CoV) is low and the exact reason for the low prevalence is not known. A total of 31 pediatric MERS-CoV cases were reported since June 2012. Of all the cases 13 (42%) were asymptomatic and the male to female ratio was 1.7:1. The mean age of patients was 9.8 ± 5.4 years.The most common source of infection was household contact followed by infection within a health care facility. Using real time reverse transcriptase polymerase chain reaction of pediatric patients revealed that 9 out of 552 (1.6%) was positive in the Kingdom of Saudi Arabia.

INTRODUCTION

Middle East respiratory syndrome-coronavirus (MERS-CoV) was first isolated in 2012 from a patient in the Kingdom of Saudi Arabia (KSA)[1]. As more cases were reported, the case fatality rate changed to 40% from 60%[2-5]. In addition, initially there was a predominance of males; later this ratio decreased[2,6]. MERS-CoV is characterized by three different patterns of disease: Sporadic cases, intra-familial transmission[7-9] and health care associated infection[2,3,10-16]. Despite the increased number overtime and the multiple health care associated outbreaks[17], the number of pediatric cases remained low during the study period[18]. The initial description of 47 cases included only a 14-year-old child[4]. The first pediatric case was a 2-year-old child reported from Jeddah, KSA on June 28, 2013[19]. Later an additional three asymptomatic children were reported[4]. The largest report of childhood MERS-CoV cases included eleven, of which two patients were symptomatic and nine were asymptomatic[18]. The exact reason for this low prevalence of the disease in children is not known. In this study, we summarize the reported MERS-CoV cases and the associated clinical presentation and the outcome.

MATERIALS AND METHODS

We searched the Saudi Ministry of Health website[20], the World Health Organization website[21], the Flutracker website[22], the medical literature and the retrieved published studies for any childhood MERS-CoV infections. We searched MEDLINE and PubMed for the keywords Middle East respiratory syndrome-coronavirus, MERS-CoV, in combination with pediatric, children, childhood, infancy and pregnancy from the initial discovery of the virus in June 2012 until April 19, 2016. The retrieved articles were also read to find other relevant articles.

RESULTS

DISCUSSION

Despite the total number of MERS cases increasing, especially in KSA, the number of pediatric cases remained low during the study period. Initially, the testing in KSA was directed towards hospitalized patients with severe pneumonia. In 2015, the Saudi Ministry of Health added a specific case definition for MERS-CoV infection in children[30]. The definition includes those ≤ 14 years, meets the adult case definition and has either a history of exposure to a confirmed or suspected MERS-CoV in the proceeding 14 d or a history of contact with camels or camel products in the proceeding 14 d[30]. The case definition also includes children with unexplained severe pneumonia[30]. The 2015 change in the case definition does not account for the low rate of childhood MERS-CoV infection as 33% of the cases were reported in 2014 before the case definition was changed. One of the reasons for an increased number of cases in 2014 during the Jeddah outbreak was increased testing of asymptomatic and mildly symptomatic patients[11].

The pattern of MERS-CoV pediatric cases was similar to the 2003 SARS outbreak. Children were less affected than adults and children less than 2 years of age had milder disease[31]. In the largest screening of contacts, the rate of MERS-CoV positive children (1.6%, 9/616) compared to 2.2% (99/4440) in adults (P = 0.23)[23]. Thus, in this study utilizing MERS-CoV PCR the positivity rate did not differ in children and adults.

In adults with MERS-CoV infections, three patterns of transmissions were observed: Sporadic (primary) cases presumed to be due to animal exposure (mainly camels), household contacts or health care associated infections[32]. In KSA, the majority (45%) of cases were health care-associated infections, 38% were primary cases, and 13% were household contacts[32]. In contrast, in the majority of pediatric cases that reported source of acquisition (66.7% of the 15 with reported source), the disease was acquired through household contact. This pattern indicates a low exposure of children to animals and a higher rate of health care associated infections in adult wards. The male to female ratio (2.8:1 and 3.3:1) was initially high[3,4]. This apparent male predominance could be explained by the nature of hospital outbreaks[2]. Eventually the male to female ratio was reduced to 1.3:1 to 1.8:1[5,6]. Consistent with these studies, the male to female ratio in children with MERS-CoV was 1.7:1 and may indicate similar exposure of children to index cases in the household settings and differential host factors.

Possible explanations for the lower number of pediatric cases compared to adults include differential testing of adult patients and milder diseases in children; although, serologic testing of pediatric patients in KSA and Jordan did not reveal any positive cases[24,25]. In the largest sero-epidemiologic survey in KSA, the study did not include children and thus it is difficult to establish the rate of sero-positivity in children[31].

The MERS-CoV infection rate in children remains low and possible explanations include: A milder disease in children, asymptomatic infection, or the presence of yet to be identified factors. The development of a shorter duration of MERS in children is another possible explanation. If this is the case, it may limit the development of a positive serology. In one study, delayed antibody responses as measured with the neutralization test was associated with severe diseases[33]. The longevity of antibodies in MERS-CoV cases might be limited as was the case with SARS[33,34]. The only study of serology among children was done among hospitalized pediatric cases who presented with lower respiratory tract infections[25]. There is no systematic screening of exposed children using serologic testing; this limited the interpretation of available serologic studies.

Little data also exist regarding the effect and the likelihood of MERS-CoV in pregnancy. Eight cases were reported[26,27,29]. The outcome was favorable in the majority of cases. The exact prevalence of MERS-CoV antibodies and exposure of pregnant women to MERS-CoV is not known.

In conclusion, the number of MERS-CoV infections in pediatric patients remains low. Possible explanations include low exposure, presence of asymptomatic, mildly symptomatic patients or the presence of yet to be identified factors. The immune system predisposing to severe disease and to fatal outcome remains unknown. An exploration of the virus-host interaction may add to the understanding of the low prevalence in this age group.

COMMENTS

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