Seasonal epidemiological and clinical characteristics of pediatric patients with human parainfluenza virus infection by serotype: a retrospective study

Pediatric patients (< 19 years of age) admitted to the Department of Pediatrics at Daejeon St. Mary’s Hospital (Daejeon, Republic of Korea) between January 2015 and December 2021 and underwent evaluations for respiratory viruses using a multiplex PCR test were recruited for this study. Among them, the patients who were positive for HPIV infections were included in this study. Patients who were positive for two or more HPIV serotypes simultaneously were excluded from the study analysis because they could have combined clinical manifestations of the different serotypes. If the same HPIV serotype was identified within 4 weeks after a previous HPIV infection, that episode was excluded, considering prolonged shedding of HPIV unrelated to current symptoms. The electronic medical records of the included patients were retrospectively reviewed to collect the demographic data, including sex and age; clinical data, including the presenting symptoms, diagnosis on discharge, breath sounds, and severe complications (receiving oxygen therapy or intensive care); laboratory data, including the complete blood count, erythrocyte sedimentation rate, and C-reactive protein, aspartate transaminase, alanine transaminase, and lactate dehydrogenase levels; and chest x-ray findings. For the diagnosis on discharge, URI was diagnosed when the patient complained of any respiratory symptoms without abnormal breath sounds and chest x-ray findings. Croup was diagnosed when the patient presented with barking cough and hoarseness with or without stridor. LRI was diagnosed when the patient complained of any respiratory symptoms, which were accompanied by abnormal breath sounds or abnormal chest x-ray findings. Among the LRIs, pneumonia was diagnosed when the chest x-ray abnormality was segmental or lobar consolidation; otherwise, bronchitis/bronchiolitis was diagnosed. If a patient experienced LRI following croup, each episode of croup and LRI was assigned separately. Febrile patients without any respiratory symptoms, abnormal physical examination, and abnormal chest x-ray findings were diagnosed with fever without localizing signs (FWLS). The month, season, and year of the diagnosis of HPIV infection were investigated. Because Korea is located in a northern temperate area, four seasons were defined as follows: spring, March to May; summer, June to August; autumn, September to November; and winter, December to February. The included patients were divided into four groups according to the identified HPIV serotype: the HPIV-1, HPIV-2, HPIV-3, and HPIV-4 groups. For the entire study population, including the patients with a single HPIV infection and those with a co-infection of HPIV and other respiratory viruses, the monthly and seasonal distributions of each HPIV serotype were determined. The clinical characteristics of HPIV infection were determined and compared among the four patient groups in patients with a single HPIV infection only, considering confounding effects of other co-identified viruses. The present study protocol was reviewed and approved by the Institutional Review Board of Daejeon St. Mary’s Hospital, which waived the need for informed consent (approval No. DC22RASI0020).

Multiplex PCR tests for respiratory viruses were performed on nasopharyngeal swabs using a commercially available Allplex Respiratory Panel 1/2/3 kit (Seegene Inc., Seoul, Republic of Korea). The Allplex Respiratory Panel 1/2/3 kit is a one-step real-time RT-PCR assay based on multiple detection temperature technology [20], and simultaneously identifies 16 respiratory viruses in a single fluorescence channel without melting curve analysis: HPIV (types 1–4), adenovirus, bocavirus, coronavirus (229E, NL63, and OC43), enterovirus, human metapneumovirus, influenza A and B viruses with subtyping, respiratory syncytial virus (RSV; groups A and B), and rhinovirus. Nucleic acid extraction was performed using a GeneAll® Viral DNA/RNA Extraction kit (GeneAll Biotechnology Co., Seoul, Republic of Korea) according to the manufacturer`s instruction. Real-time RT-PCR was performed using a CFX96 real-time PCR detection system (Bio-Rad, Hercules, CA, USA). Automated analysis of the results was performed using a Seegene Viewer software (Seegene Inc.). Samples were considered positive when the cycle threshold was < 42.

The monthly and seasonal distributions of each HPIV serotype were determined for the 514 episodes of HPIV infection (Fig. 1). Because of the pandemic of coronavirus disease 2019 (COVID-19), only 3 and 26 episodes were identified in 2020 and 2021, respectively. Before the COVID-19 pandemic in 2015–2019, HPIV-3 was the most prevalent of four serotypes every year, with annual peaks between April and June (Fig. 1A). HPIV-1 showed a less-prominent seasonal peak than HPIV-3, and HPIV-2 and HPIV-4 showed various seasonal patterns in each year (Fig. 1A). However, over the study period, HPIV-1, HPIV-2, and HPIV-4 showed seasonal peaks in autumn (Fig. 1B). During the COVID-19 pandemic in 2021, HPIV-3 showed a seasonal peak in autumn, which was different from previous epidemical patterns for this serotype (Fig. 1A).

The clinical characteristics of HPIV infection were evaluated in 190 patients with a single HPIV infection, and they were compared among the HPIV-1, HPIV-2, HPIV-3, and HPIV-4 groups (Table 1). The patients in the HPIV-1 and HPIV-3 groups were younger than those in the HPIV-2 and HPIV-4 groups (P < 0.001). Most patients in the HPIV-1 and HPIV-3 groups were aged < 36 months, while about half of the patients in the HPIV-2 and HPIV-4 groups were aged ≥ 36 months (Table 1). Fever developed least frequently (P < 0.001) and fever duration was shortest (P = 0.005) in the HPIV-4 group (Table 1), whereas, sputum was accompanied by HPIV infection most frequently in the HPIV-4 group (P = 0.001, Table 1). Each virus type caused a range of illnesses, from FWLS to pneumonia (Table 1). Croup was diagnosed most frequently in the HPIV-1 group (P < 0.001), while none in the HPIV-4 group were diagnosed with croup (Table 1). About half of the patients in the HPIV-2 and HPIV-3 groups were diagnosed with URI, whereas ≥ 70% of the patients in the HPIV-1 and HPIV-4 groups were diagnosed with croup or LRI (Table 1). LRI developed most frequently in the HPIV-4 group (p = 0.002). Accordingly, abnormal breath sounds and chest x-ray abnormalities were more frequent in the HPIV-1 and HPIV-4 groups than in the HPIV-2 and HPIV-3 groups (P = 0.004, Table 1). However, severe complications were rare, and their frequencies were comparable among the four groups. There were no significant differences in the laboratory test results among the four groups.

During the COVID-19 pandemic in 2020–2021, 12 (80.0%) of 15 single HPIV infections were caused by HPIV-3. Significantly more patients in the HPIV-3 group were diagnosed with URI during the COVID-19 pandemic than before the COVID-19 pandemic (83.3% vs. 38.9%, P = 0.004, Table 2). Therefore, the frequencies of abnormal breath sounds (P = 0.048) and chest x-ray abnormalities (P = 0.007) decreased significantly during the COVID-19 pandemic compared with before the pandemic (Table 2). In addition, more patients experienced seizures during the COVID-19 pandemic than before the COVID-19 pandemic (50.0% vs. 2.8%, P < 0.001, Table 2).