Clinical and Epidemiologic Characteristics of Infants Hospitalized with Respiratory Syncytial Virus Infection During the 2022-2023 Season in Mexico.

In 2022, several countries reported an increase in respiratory syncytial virus (RSV) infections. We assessed the clinical characteristics and outcomes of infants hospitalized with RSV and compared them with infants hospitalized between 2009 and 2015. No significant differences in underlying disorders, intensive care unit admission rates and mortality were observed suggesting currently circulating RSV strains do not show heightened virulence.

Incidence of congenital and postnatal cytomegalovirus infection during the first year of life in Mexican preterm infants.

Cytomegalovirus infection occurs commonly during infancy. Postnatal infection in term infants is usually asymptomatic; however, infection in preterm infants can be associated with clinical manifestations during the neonatal period. Nevertheless, few studies to assess the frequency of cytomegalovirus infection in preterm infants have been performed outside of high-income countries. We analyzed the incidence of congenital and postnatal cytomegalovirus infection in a cohort of preterm infants. Cytomegalovirus infection was detected during the neonatal period in four of 178 infants; in three of them, the virus was detected during the first 3 weeks of life and, therefore, congenital infection was confirmed (1.7% incidence). Postnatal infection was detected in 44 (36.4%) of 121 infants who were assessed after discharge from the neonatal intensive care unit. Cytomegalovirus infection was significantly associated with the duration of breastfeeding. In addition, we characterized cytomegalovirus strains detected in infants together with sequences available at GenBank, based on sequences of the UL18 gene. Cytomegalovirus UL18-sequences clustered in five distinct clades (A-E), and sequences obtained from infants in our study were distributed in four of the five clades; 44.4% of these sequences were included in clade E. Breastfeeding duration was shorter on average (5.6 months) in infants with sequences in clade E compared to infants with sequences in the other three clades (8.2 months; p = .07). In conclusion, we provide information regarding the high incidence of cytomegalovirus infection in preterm infants. Further studies are warranted to assess if cytomegalovirus strain characteristics are associated with the risk of infection acquisition during infancy.

Respiratory syncytial virus acute respiratory infection-associated hospitalizations in preterm Mexican infants: A cohort study.

BACKGROUND: Respiratory syncytial virus (RSV) is the leading cause of severe acute respiratory infections (ARI) in preterm infants. The incidence of RSV-associated hospitalizations has not been defined in Mexico. OBJECTIVES: To determine the incidence of ARI- and RSV-associated hospitalizations in preterm infants during the first year of life. METHODS: Prospective cohort study of 294 preterm infants followed up through monthly telephone calls and routine outpatient visits. Hospitalized children were identified through daily visits to pediatric wards of participating hospitals and through telephone calls. Respiratory samples were tested for RSV by RT-PCR. RESULTS: Mean gestational age of participating infants was 33 weeks. Ninety-six infants were diagnosed with bronchopulmonary dysplasia (BPD) and 17 with congenital heart disease (CHD); 11 had both conditions. There were 71 hospitalization episodes in 53 infants. Respiratory samples for RSV detection were available in 44 hospitalization episodes, and the result was positive in 16 (36.3%). At least one hospitalization for ARI was recorded in 33 of 96 participants with BPD, in seven of 17 with CHD, and 18 of 192 infants without these diagnoses. Five (71.4%) of CHD infants who required admission also had BPD. RSV-confirmed hospitalization rates were 9.4%, 5.9%, and 2.6% for infants with BPD, CHD, and otherwise healthy preterm infants, respectively. Attributable RSV admission frequencies were estimated to be 13.6%, 16.5%, and 4.1%, respectively. CONCLUSIONS: Mexican preterm infants, particularly those with BPD, have high rates of ARI- and RSVassociated hospitalizations. Specific interventions to reduce the incidence of severe infections in this highrisk group are required.

Effect of cytomegalovirus infection and leukocyte immunoglobulin like receptor B1 polymorphisms on receptor expression in peripheral blood mononuclear cells.

Leukocyte immunoglobulin like receptor B1 (LILRB1) plays a significant role in a number of infectious, autoimmune, cardiovascular, and oncologic disorders. LILRB1 expression varies between individuals and may be associated with polymorphisms on the regulatory region of the LILRB1 gene, as well as to previous cytomegalovirus infection. In this study, the contribution of these two factors to LILRB1 expression in peripheral blood mononuclear cells of healthy young adults was analyzed. LILRB1 expression in NK cells, T cells, B cells and monocytes was significantly stronger in individuals who had had cytomegalovirus infection than in those who had not (P < 0.001, P < 0.001, P < 0.01, and P < 0.001, respectively). Overall, no differences in LILRB1 expression were observed between individuals with and without GAA haplotypes of the LILRB1 regulatory region. However, when analyzed according to cytomegalovirus infection status, significant differences in LILRB1+ NK cells were observed. A higher proportion of LILRB1+ cells was found in GAA+ than in GAA- individuals who had not been infected (P < 0.01), whereas GAA- individuals had a larger proportion of LILRB1+ cells than GAA+ individuals who were cytomegalovirus positive (P < 0.01). In conclusion, cytomegalovirus infection has a major effect on LILRB1 expression in NK and other mononuclear cells and polymorphisms in the LILRB1 regulatory region appear to have a modulatory influence over this effect.

Respiratory Syncytial Virus-A ON1 Genotype Emergence in Central Mexico in 2009 and Evidence of Multiple Duplication Events.

Background: Respiratory syncytial virus (RSV) is a leading cause of respiratory infections. An RSV-A genotype (ON1) that contains a 72-nt duplication was reported in 2012 and has since extended worldwide. Methods: We analyzed 345 respiratory samples obtained between 2003 and 2014 to assess the relevance of ON1 infections. Nucleotidic and deduced amino acid sequences from viruses detected in San Luis Potosí and sequences previously reported were analyzed. Results: RSV ON1 was detected in 105 samples. The earliest case of ON1 infection was detected in November 2009, almost 1 year prior to detection of this virus in Canada. Amino acid sequence analysis of the duplication region showed the presence of Y273N and L274P substitutions in RSV GA2 viruses that, when combined, resulted in 4 different GXXSPSQ sequence motifs at positions 272-278. Three of these motifs were present in both the original and duplicated regions of ON1 strains. Additional signature amino acid substitutions were observed in ON1 strains that have the different sequence motifs. Conclusions: ON1 strains include viruses that appear to be the result of at least 3 independent duplication events. Molecular data of strains from diverse geographical regions should help define the frequency and implications of this evolution mechanism.

NK cell immunophenotypic and genotypic analysis of infants with severe respiratory syncytial virus infection.

Respiratory syncytial virus (RSV) is the leading cause of severe lower respiratory tract infection in infants. Reduced numbers of NK cells have been reported in infants with severe RSV infection; however, the precise role of NK cells during acute RSV infection is unclear. In this study the NK and T cell phenotypes, LILRB1 gene polymorphisms and KIR genotypes of infants hospitalized with RSV infection were analyzed. Compared to controls, infants with acute RSV infection showed a higher proportion of LILRB1+ T cells; in addition, a subgroup of infants with RSV infection showed an increase in LILRB1+ NK cells. No differences in NKG2C, NKG2A, or CD161 expression between RSV infected infants and controls were observed. LILRB1 genotype distribution of the rs3760860 A>G, and rs3760861 A>G single nucleotide polymorphisms differed between infants with RSV infection and healthy donors, whereas no differences in any of the KIR genes were observed. Our results suggest that LILRB1 participates in the pathogenesis of RSV infection. Further studies are needed to define the role of LILRB1+ NK in response to RSV and to confirm an association between LILRB1 polymorphisms and the risk of severe RSV infection.