Enterovirus D68 (EV-D68) belongs to the family Picornaviridae. It is part of the many types of enteroviruses, a group of single-stranded RNA (ssRNA), non-enveloped viruses. Distinct from all other enteroviruses, EV-D68 exhibits acid lability and a lower optimum growth temperature which is similar to that of human rhinoviruses. The classified enterovirus 68 is a member of group D enteroviruses, hence the name EV-D68. The EV-D68 genome contains a single open reading frame which codes for a polyprotein that is cleaved into four viral capsid proteins VP1–VP4 and seven non-structural proteins 2A–2C, 3A–3D.¹

During the past few years, EV-D68 has emerged as a major viral pathogen leading to heightened alertness with recent outbreaks occurring in the United States,² Canada,³ Chile,⁴ as well as in several other countries in Europe⁵ and Asia.⁶ The virus is known to cause a spectrum of symptoms including sore throat, cough, breathing difficulties and central nervous system (CNS) clinical signs that may be confused with influenza.^7,8,9 The virus has also been shown to represent a considerable proportion of the pathogens associated with acute respiratory infections (ARI), mostly upper respiratory tract infections (URTI).¹⁰ ARI is a very serious infection of the upper respiratory tract and presents mostly with difficulty in breathing. It is mainly common in children younger than 5 years and shares symptoms with Influenza-Like Illness (ILI) – which is commonly associated with patients younger than 2 years – such as fever or sore throat, cough and nasal congestion with pneumonia being a complication. ILI causes a set of common symptoms that could be influenza or other illness; it represents the outpatient department cases specifically for this study. Severe acute respiratory infection (SARI) is an ARI that shows a recent onset of fever (≥ 38 °C) within 7 days, cough and shortness of breath or difficulty in breathing which requires hospitalisation. Children younger than 5 years and others with asthma are prone to the predisposing factors,¹¹ as are adults with asthma and immunosuppression. Enterovirus D68 caused outbreaks of respiratory illnesses in the United States in August 2014; in the middle of October 691 people in 46 states and the District of Columbia were attacked with a respiratory tract infection (RTI) brought about by EV-D68.¹¹ A huge number of children in Canada also had the disease, with a base loss of life of 14.¹²

For over two decades now, phylogenetic analyses of the sequences of all EV-D68 reported to CDC and WHO show that multiple clades of the virus have emerged and are currently circulating and contributing to respiratory disease globally.¹³ The EV-D68 strain responsible for the 2014 episode was new and had no or little reference, even though similar outbreaks had occurred over the years,^14,15. Consequently, phylogenetic analysis of EV-D68 strains from the 2014 episode could give cutting-edge data in regard to the development status of the infection. However, epidemiological data about this virus especially on the African continent is limited. An analysis of archived and novel EV-D68 strains from patients with respiratory disease in Africa and the United States was performed and the results indicated that several recently emerged distinct clades are circulating globally.¹⁶ As there is currently no vaccine and definite treatment against EV-D68 infection, management of the infection is through symptomatic treatment.

The National Influenza Centre (NIC) in Ghana conducts laboratory surveillance for RTIs in Ghana which mainly focuses on influenza viruses. Data generated so far indicated a high burden of ARI in children. Between January 2014 and March 2015, the NIC received 2801 presumptive ILI and 2856 presumptive SARI cases across the country for processing. Real time transciption-polymerase chain reaction (RT-PCR) results indicated positivity rates of 10.5% among ILI cases and 14.5% among SARI cases, leaving a large proportion of samples with unknown aetiology. The recent EV-D68 outbreak has necessitated the need to re-examine the role that the virus may play as a potential cause of severe respiratory illness and the possible neurologic effects.

As part of a retrospective study to identify the aetiology and clinical characteristics of viral RTIs in influenza virus-negative samples, we probed these negative influenza cases in all children, both outpatients and inpatients, from influenza sentinel hospitals throughout Ghana in 2014 for EV-D68 to determine and describe their association with ARIs.

A total of 182 archived respiratory samples (OP or NP) were obtained from the NIC between January 2014 and December 2015 (Figure 1). The mean age was 8 years within a range of 1 month to 15 years, of which 102 (56%) were male with an average age of 1 year. Females contributed 80 (44%) samples with an average age of 1 year (Table 2). There were more specimens (45.5%) from patients in the 1 year or younger age group than any other age group. Specimens were from 9 out of 10 regions in Ghana. One hundred and sixty-three (163/182) patients showed fever with no less than one respiratory manifestation. The most common respiratory symptom was cough (89.6%) with each of other symptoms revealed in under half of samples (Figure 2). Myalgia was the slightest detailed indication (2.2%). Two specimens were from patients with pre-existing medical conditions of asthma (1) and pneumonia (1). The majority (99%) of samples were collected within 7 days of ailment onset.

The prevalence of EV-D68 infections in respiratory specimens reported in literature range from 1% to 36% mainly due to differences in study areas and studied populations.¹⁶ In this study, EV-D68 was detected in 2.2% of archived respiratory specimens from patients with ARI in Ghana which is consistent with the range in literature. Our findings are consistent with another study conducted in Spain where the laboratory confirmed that EV-D68 could be established in approximately 2.5% of tested episodes in both hospitalised children and outpatients.¹⁹ Contrary to this, a study in France in 2009–2010, however, detected 63% EV-D68 among hospitalised children aged 6 months to 10 years.²⁰

Association of EV-D68 infections with seasonality have been published in several studies, although there are variations in regional and annual circulation of different EV-D68 types.¹⁸ Although there is not enough evidence to describe seasonality of EV-D68 in relation to climate in the northern and southern parts of Ghana, data from this study interestingly reveal that circulation of EV-D68 occurs all year round in Ghana as shown in Figure 1. Detection frequency peaked in the third and fourth quarters with no detection in the first and second quarters.

Midgley et al (2014)¹¹ reported a higher rate of EV-D68 detection among children in the 1–5 years range. Similarly, this study detected EV-D68 more frequently among children younger than 5 years (Table 3). The highest number of EV-D68 positive cases was recorded for the 1–5 years age group although this was statistically insignificant (p > 0.05) as shown in Figure 3. As shown in Table 2, EV-D68 was detected more frequently in SARI cases (1.6%) than in ILI case (0.5%). This correlates with other studies where detection of EV-D68 in ILI cases was less but infection was high in hospitalised patients. The low EV-D68 detection rate in outpatients is similar to some studies published.²⁰ CDC reports URTI as the most common clinical presentation during EV-D68 infections. In this study, all EV-D68 positive samples were from patients with URTI, which confirms the contribution of EV-D68 as a major viral agent in URTI. Clinical signs reported in EV-D68 associated ARI included fever, cough, sore throat, rhinorrhoea, and headache, which is consistent with other studies.^11,21