Adenovirus Respiratory Infections Post Pandemic in Colombia: An Old Enemy With Increased Severity in Pediatric Population?

To the Editors: In Colombia and around the world, the risk of common respiratory infections has been lower due to preventive nonpharmacologic strategies. The prevalence of different respiratory viruses increased after the pandemic when several nonpharmacologic strategies were no longer applied. These changes could be explained by decreased immune stimulation and childhood vaccine coverage as well as by weaning immunity.1 Respiratory syncytial virus (RSV), influenza, rhinovirus, parainfluenza, adenovirus (AdnV) and enterovirus are the major causes of respiratory infections requiring hospitalization in children. However, AdnV has not been the predominant respiratory virus.2,3 Several countries, including the United States, have recently issued health alerts due to an increase in the frequency and severity of RSV and influenza infections.4 In contrast, in Colombia, we have seen an unusual and concerning pattern of AdnV respiratory infections. In Colombia, during the first 6 months of 2022, RSV was the leading respiratory pathogen, with a frequency of 28.1%, and AdnV was the fourth leading respiratory pathogen, with 16.9%5 of the cases. Nevertheless, the rate of AdnV detection has increased substantially since August, becoming the second most frequently identified virus, surpassed only by rhinovirus/enterovirus (Fig. 1A), with positivity rates ranging between 22.7% in August and 32.5% in October.FIGURE 1.: Distribution of viral isolates in patients with viral infections in Colombia in 2022. A: Percentage distribution of viruses identified in severe respiratory infection by month in a pediatric reference center in Bogotá, Colombia 2022 (n = 3381). B: Number of patients requiring ECMO and corresponding virus, RSV and AdnV circulation, and cases of IPDs in a reference center in Bogotá, Colombia in 2022 (n = 25). IPD indicates invasive pneumococcal disease; PIV, parainfluenza virus; R/EV, human rhinovirus and enterovirus; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.Regarding disease severity, preliminary data from the Bogotá Secretary of Health showed that the incidence of pneumonia-related deaths in children under age 5 increased by 103% in September when compared with the incidence at the same period in 2019 (26 vs. 53), with a rate of 5.3 versus 10.9 × 100,000 children under 5 years of age. Etiology was identified in 26 cases; 12 (46%) were attributed to AdnV and 10 (38%) to RSV; in 9 cases, coinfection with pneumococcus was reported. In Bogotá, 46% of the deaths were children between 1 and 2 years of age, and 80% of patients did not present underlying conditions. From June 2022 to November 2022, AdnV accounted for 24% to 45.8% of hospitalizations in the pediatric intensive care unit. In several cities, we have identified a greater severity of respiratory infections. In a reference center in Bogotá during 2022, 25 patients required extracorporeal membrane oxygenation (ECMO), compared with only 2 in 2021. Of those, AdnV was detected in 76% (19/25). Another center had 17 ECMO patients, and 65% (11/17) required ECMO due to AdnV. We also noted an increase in antimicrobial use in cases of invasive pneumococcal diseases (Fig. 1B), which had not been previously described. Researchers in Colombia have reported that the incidences of bronchiolitis obliterans and other complications, such as hemophagocytic syndrome, have also increased. Biphasic behavior and findings consistent with multisystem inflammatory syndrome “associated” with AdnV, like the syndrome described with severe acute respiratory syndrome coronavirus 2, have been reported. The Bogotá Secretary of Health has reported increased use of intravenous immunoglobulin G in several of the deceased cases, more frequently in AdnV-related patients compared with RSV infections, probably associated with a severe inflammatory response and cardiac compromise in some cases. The increased severity of AdnV infections could be explained by a lack of immunity or the presence of new virulent serotypes, among others. Local and national surveillance must be reinforced to continue monitoring this phenomenon and to facilitate the implementation of transmission prevention, diagnosis and treatment strategies.