Abstract Background Although parainfluenza virus type 4 (PIV-4) typically causes mild respiratory illnesses in children, it can cause severe diseases occasionally. It is not known Whether viral load of PIV-4 could correlate with severity. This study aimed to assess the relationship between PIV-4 viral load and disease’s severity in children. Viral load and severity This figure shows the relationship between severity of illness and viral load.There was no correlation between viral load and severity. Methods A retrospective study at Tokyo Metropolitan Children's Medical Center from April to October 2023 screened hospitalized children using multiplex PCR. PIV-4 positive samples were assayed for viral load of all detected viruses using real-time PCR. Cases with PIV-4 were included if PIV-4 was only detected or the viral load of PIV-4 was higher than other co-detected viruses. Demographic data, underlying diseases, laboratory, co-infections, diagnoses, and outcomes were collected from electrical charts. Cases with PIV-4 were categorized into mild cases with no oxygen demand, moderate cases with low-flow oxygen demand and severe cases with high flow nasal cannula oxygen or non-invasive/invasive mechanical ventilation or PICU admission.The viral loads of PIV-4 and number of co-infected virus were compared among severity groups. Characteristics, Symptoms and Laboratory Data of PIV-4 positive patients Results Nasal swab samples were collected from 2884 cases. PIV-4 was detected in 185 samples. As 108 cases were excluded for higher viral loads of other viruses, 77 cases were included for analysis. The severity of PIV-4 comprised 37 mild, 24 moderate, and 16 severe cases. The rate of lower respiratory tract infections in mild, moderate and severe cases were 8%, 96%, and 75%, respectively. There was only one PIV-4-related mortality at 28 days. Co-detection with rhinovirus/enterovirus was the most frequent. Median viral loads (log10 copies/mL) in mild, moderate and severe cases were 5.98 (IQR 3.58-6.89), 6.09 (IQR 4.93-6.66) and 5.98 (IQR 3.57-7.03), respectively. No significant correlation was found between viral load and severity, but severity correlated with the number of viral co-infections. Treatment and Outcome of PIV-4 positive patients Conclusion Moderate or severe Pediatric PIV-4 infections primarily show as lower respiratory tract infections, with no relation between viral load and illness severity, though the number of co-infected virus may play a role. Severity and co-infection viruses Disclosures All Authors: No reported disclosures
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