Respiratory Syncytial Virus-associated hospitalization in premature infants who did not receive palivizumab prophylaxis in Italy: a retrospective analysis from the Osservatorio Study.

BACKGROUND Due to different social and epidemiological factors, the eligibility criteria to receive palivizumab prophylaxis may be different between countries, especially in "otherwise healthy" late preterm infants. METHODS We analyzed an Italian database of young children referred to emergency departments for acute lower respiratory tract infection (ALRI) during the RSV season over a four year period, when the use of palivizumab as prophylaxis for RSV disease was not widespread in premature infants. The demographic and environmental characteristics and the RSV positivity (RSV(+)) in hospitalized and not-hospitalized patients were compared. In the data analysis we divided children according to their chronologic age (age) and their week gestational age (wGA). RESULTS Out of the 100 children evaluated, 68 were infants (≤12 month-age): 7.5 and 20.6 % were in the <29 and 29- < 32 wGA groups respectively, and 72.0 % in the 32- < 35 wGA group. Positive hospitalized-to-not-hospitalized ratios were found in all three wGA groups, progressively decreasing (from 4.0 to 1.2), with increasing wGA (p = 0.35). The percentage of hospitalized infants that were also RSV(+) was also progressively decreasing (from 40.0 to 28.6 % and 18.4 %) with increasing wGA (p = 0.43). In the >12 month-age group (N = 32), there was positive hospitalized-to-not-hospitalized ratio only in the <29 wGA group with a low RSV(+) frequency (<29 %) in all wGA groups. In the ≤12 month-age group, 41 infants were evaluated with a ≤6 month-age and 27 with a >6-12 month-age. A positive hospitalized-to-not-hospitalized ratios was found in all wGA groups in ≤6 month-age infants, despite a low RSV(+) frequency in the 29- < 32 and 32- < 35 wGA group. In the >6-12 month-age group, all infants with a <29 and 29- < 32 wGA were hospitalized with a relatively high RSV(+) frequency whilst the 32- < 35 wGA group showed a negative hospitalized-to-not-hospitalized ratio with a lower RSV(+) frequency. CONCLUSIONS The hospitalized-to-not-hospitalized ratios and RSV(+) frequency in the first 12 months of age in infants born prematurely confirm the vulnerability of these children for clinically important RSV infection, most notably in the <32 wGA category.