Preterm infants are at high risk for rehospitalization due to respiratory illness. We found that 30% of children under the age of two admitted to the PICU for respiratory diseases were born prematurely. Although a larger proportion of these infants were classified as early preterm (17%), late preterm infants also accounted for a significant proportion (12%) of admissions. Males were overrepresented in both the EPT and LPT groups compared with the FT group, which is similar to the sex disparity described for chronic lung disease of prematurity (14
). Lower respiratory tract infection accounted for over 50% of admissions in all three groups, with RSV being the most common infectious organism. Preterm infants had longer PICU and hospital lengths of stay, utilized more hospital resources, and incurred higher total hospital charges compared with FT infants. Remarkably, LPT infants had similarly high lengths of stay and hospital charges as EPT infants, suggesting that resource utilization was similar between for EPT and LPT infants admitted to the PICU.
These findings are important because our data show that not only do children born preterm comprise a substantial proportion of admissions to the PICU for respiratory illness in the first years of life, but they consume considerably more hospital resources and incur more charges than full term infants. The fact that preterm infants represented almost one-third of respiratory admissions to our PICU is significant considering that in 2004, preterm infants accounted for 12.5% of all births (13
). In addition, the proportion of preterm infants in this study represents an estimation of late morbidity rather than early morbidity because our institution frequently admits premature infants less than 44 weeks post-conceptional age back to the neonatal intensive care unit, and those infants were not included in this study. The fact that preterm infants are at high risk for rehospitalization has been well-reported in the literature (2
) but few studies have examined the morbidity incurred once admitted, or the clinical course. It is notable that among the infants admitted to the PICU, LPT infants had similarly high morbidity as did EPT infants, which appears contrary to the commonly held assumption that LPT infants have a morbidity risk profile more closely approximate to that of FT infants. This information should be utilized for both preventive strategies and prognostication, and provides more evidence for labeling infants in this gestational age group as late preterm rather than near-term.
Recent studies have also found that LPT infants are a population at risk for increased morbidities, cost, and rehospitalization when compared with FT infants. Khashu et al reported that perinatal respiratory morbidity among LPT infants was 4.4 times greater than in FT infants and that infections were 5.2 times more common (9
). Another study evaluating morbidity in the first year of life found that 15.2 % of LPT infants were rehospitalized compared with 7.9% of FT infants (15
). Respiratory illness was the most common reason for rehospitalization among both groups. In addition, infants born 35 to 36 weeks' gestation were more likely than infants born ≥ 37 weeks' gestation to be rehospitalized 15 to 182 days after birth (8
). Our data support the findings of these previous studies that the LPT population should be considered a group at considerable risk for future morbidities including rehospitalization and PICU admission, and should not be considered to have risk similar to that of FT infants.
Lower respiratory tract infection was the leading cause of admission in our study with relatively few PICU admissions in preterm infants attributed to infectious airway compromise compared with FT infants. One possible explanation for this finding is that infections causing airway compromise in these groups also caused lower respiratory tract infection, and patients were primarily labeled as such in the medical record. Previous studies have found that RSV is a common etiologic agent for lower respiratory tract infection and rehospitalization in preterm infants with chronic lung disease (16
), and this was the case among the infants admitted to the PICU. Carbonell-Estrany et al found that 20% of infants born less than 32 weeks' gestation without defined chronic lung disease were rehospitalized for respiratory disease, with RSV being the causative agent in nearly 50% (17
). Additionally, preterm infants were found to constitute 30% of PICU admissions for RSV (16% EPT, 14% LPT) in Israel (5
). Because RSV is an important cause of rehospitalization and morbidity in EPT infants with or without CLD, RSV prophylaxis with palivizumab has been recommended for EPT infants and other infants with cardiac or chronic lung disease in an effort to reduce severe respiratory illness (18
). Although our study suggests that LPT infants represent a significant proportion of infants admitted to the PICU with RSV and have similar morbidities to EPT infants once admitted, we do not have admission rate data for this group of infants in order to determine the cost-benefit ratio for providing palivizumab to LPT infants. McLaurin reported that RSV was the most common cause of admission among the 15.2% of LPT infants rehospitalized in the first year of life (15
). Because morbidity is high for LPT infants who are admitted to the PICU with RSV, further studies evaluating risk factors for ICU admission in LPT infants should be performed to determine which of these infants might benefit from palivizumab prophylaxis.
These data suggest that the increased resource utilization and hospital charges, at least among LPT infants, are independent of LOS. Several areas of increased resource utilization among the PT infants were identified including increased length of ventilation (although this did not reach statistical significance), and increased orders for echocardiograms and non-respiratory cultures. The reasons for higher resource utilization in these groups may stem from the fact that many children in the EPT and LPT groups required significant medical support for both chronic respiratory and non-respiratory conditions prior to hospitalization. Greater surveillance of these special needs children including adherence to RSV prophylaxis, improved monitoring of oxygen requirement (both awake and asleep), nutritional status, and ensuring optimal home environments may help prevent late PICU admission, but requires further study. Among children without non-respiratory disorders, LPT infants had significantly greater LOS compared with FT infants which suggests that additional factors beyond these conditions influence morbidly risk. We speculate that some of these LPT infants may have had subtle health impairments that may have been under appreciated prior to rehospitalization. More specific identification of these risk factors for resource utilization after admission would allow more targeted intervention strategies for these groups.
There are several limitations to our study. First, there are inconsistent reports in the literature of the proper age definitions of early and late preterm infants. Although newer definitions of LPT infants have limited infants in this group to 34-36 weeks' gestational age birth, we chose to define early preterm as < 32 weeks' gestational age because this is the age group at greatest risk for chronic lung disease. However, we were unable to identify with certainty those infants who were diagnosed with BPD during their neonatal intensive care unit (NICU) admission because we did not have access to data from the NICU course for most patients. In addition, for many of the patients, gestational age at birth was obtained from the PICU admission history and physical, which may not be completely accurate. Due to the inconsistent recording of gestational age for infants ≥ 36 weeks' gestational age in the medical record, we chose to classify these infants as full term. Because FT infants represented a much higher proportion of study patients, there was greater power to detect differences between each of the preterm groups and the FT group than between the two preterm groups. Finally, children with non-respiratory chronic disease accounted for a large proportion of PICU admissions (nearly 50% in EPT and LPT groups), which may be responsible for some of the morbidities seen in these groups. Unfortunately, further detail of these disabilities and their impact on morbidity risk could not be obtained as part of this study.