Discussion

The current meta-analysis summarises the pooled Covid-19 symptoms frequency and distribution values related to the otorhinolaryngological domain in 24 000 paediatric patients. The commonest otorhinolaryngological symptom was cough, followed by sore throat and nasal discharge. Previous reviews^{Reference Cui, Zhao, Zhang, Guo, Guo and Zheng109} have revealed the commonest presenting symptoms in children to be fever (pooled prevalence of 51 per cent; 95 per cent CI = 45–57) and cough (pooled prevalence of 41 per cent; 95 per cent CI = 35–47). By comparison, the commonest otorhinolaryngological symptoms noted in adult patients, by Qiu et al.,^{Reference Qiu, Yang, Liu, Wu, Cui and Mou110} were olfactory dysfunction (47 per cent), sneezing (27 per cent) and nasal congestion (19 per cent). These findings highlight the differences between the otolaryngological symptom profiles of children and adults.

Cough is a common symptom of Covid-19 infection that may arise with both upper and lower respiratory involvement. We found cough to be the commonest symptom, with a pooled prevalence of 38 per cent, as reported from 94 studies. This is similar to the findings of previous reports. Though severe lower respiratory involvement often manifests with accompanying symptoms, it may be difficult to localise the focus to the upper versus the lower respiratory tract in milder cases presenting with cough. Regardless, given the potential for significant aerosol generation, cough remains an important symptom for disease transmission. In addition, the high prevalence of cough in children suggests the potential for transmissibility to other vulnerable age groups and caregivers.

Given the frequent occurrence of common cold symptoms in children irrespective of Covid-19 infection, it is possible to mistake Covid-19 infection for common cold symptoms in this age group, leading to a higher propensity of community transmission. Compared with the common cold and allergic rhinitis, nasal symptoms are less frequent in Covid-19 patients.^{Reference Bruno, Locatello, Cilona, Fancello, Vultaggio and Maltagliati111} Rhinorrhoea and nasal congestion are reported in fewer than one-fifth of Covid-19 cases.^{Reference Cui, Zhao, Zhang, Guo, Guo and Zheng109} The present analysis showed the pooled prevalence of rhinorrhoea and congestion to be 15 per cent and 8 per cent, respectively.

Olfactory and taste dysfunction is one of the most familiar manifestations of Covid-19 encountered in adults. The high rate of olfactory symptoms correlates with the neurotropism exhibited by SARS-CoV-2 towards the neuroepithelium present in the olfactory cleft. These symptoms can occur in isolation without other nasal symptoms, they typically signal a milder disease course, and they are reversible in the majority of patients.^{Reference Nguyen, Hoang, Lagier, Raoult and Gautret112,Reference Moein, Hashemian, Tabarsi and Doty113} The meta-analysis by Qiu et al.,^{Reference Qiu, Yang, Liu, Wu, Cui and Mou110} involving 54 studies and 16 478 adult patients, revealed the pooled prevalence of olfactory symptoms to be 47 per cent (95 per cent CI = 29–65). However, in the paediatric age group, the olfactory and taste symptoms are relatively infrequent. A higher prevalence is noted in older children.^{Reference Hijazi, Alaraifi and Alsaab9} This may be attributed to an age-related biological difference, or may be secondary to the inability of the children to identify or communicate these symptoms effectively. Regarding the pooled incidence, these symptoms affected less than a tenth of infected children. A recent meta-analysis by Yan et al.^{Reference Yan, Qiu, Liu, Guo and Hu114} showed the prevalence of smell and taste disturbances in children to be 15 per cent and 9 per cent, respectively. Older age and female gender were associated with a higher prevalence of smell disturbances.

Laryngeal and otological symptoms have been infrequent in adult and paediatric populations, and were described as case reports or case series. The current report showed fewer than 10 per cent of the studies reporting on the presence or absence of these symptoms.^{Reference Kilic, Kalcioglu, Cag, Tuysuz, Pektas and Caskurlu115–Reference Azzam, Samy, Sefein and ElRouby119}

The current analysis showed asymptomatic infections in almost a fourth of affected children. Previous reviews reported the proportion of asymptomatic infections as 40–45 per cent,^{Reference Oran and Topol120} while the pooled prevalence of asymptomatic cases was calculated to be 48 per cent by Syangtan et al. using a random effect model.^{Reference Syangtan, Bista, Dawadi, Rayamajhee, Shrestha and Tuladhar121} The same meta-analysis revealed the largest proportion of asymptomatic cases in children (49.6 per cent), followed by the adult (30.3 per cent) and elderly (16.9 per cent) populations. The prevalence of asymptomatic infections apparent from our data is lower (27 per cent). However, given that many asymptomatic infected individuals possibly never visited the hospital, we assume this percentage is larger than that reflected in the current data. Asymptomatic, equally infectious individuals are likely to continue spreading the infection in the community if not detected and isolated. The lower exposure rate for children compared with adults, secondary to the lack of workplace and travel-related exposures, may contribute to the lower predisposition of children to the viral infection. Once exposed, the children are equally likely as adults to acquire the infection.^{Reference Bi, Wu, Mei, Ye, Zou and Zhang122} However, the more favourable immunity profile, a different pattern of de novo angiotensin-converting enzyme 2 (ACE-2) receptor expression in the airway, or a different pattern of induction of the lower airway ACE-2 receptor after homing of the virus to the upper airways in children may underlie the higher rate of ‘asymptomatic’ infections.^{Reference Bunyavanich, Do and Vicencio123,Reference Fialkowski, Gernez, Arya, Weinacht, Kinane and Yonker124} The usual lack of associated co-morbidities in children is also protective.