Rehospitalization for Respiratory Illness in Infants of Less Than 32 Weeks' Gestation

(1)

and without chronic lung disease. Pediatrics 1991;88:527â€”

532; preterm infant, rehospitalization, respiratory illness.

ABBREVIATIONS.BPD, bronchopulmonarydysplasia;NICU,

neonatal intensive care unit; RSV, respiratory syncytial virus; VLBW, very low birth weight.

It is known that preterm infants are at increased risk for rehospitalization after nursery discharge'3 and that respiratory illness is the most common reason for admission.' More than 40% of infants with bronchopulmonary dysplasia (BPD) will re quire rehospitalization during the first year of life because of acute viral respiratory tract infec tions46; however, the incidence of serious illness in preterm infants with little or no lung disease in the neonatal period has not been studied extensively. Furthermore, the impacts of the season of neonatal intensive care unit (NICU) discharge and the age ofthe infant during the first respiratory viral season on the risk of rehospitalization are not known.

We prospectively studied rehospitalization for respiratory illness among a cohort of preterm in fants and a socioeconomically matched full-term group. We compared the incidence of hospitaliza tion for preterm infants with and without BPD and

examinedneonataland environmentalfactorsthat

predispose preterm infants to serious respiratory illness.

ABSTRACT.All 133survivinginfantsof gestationalage

s32 weeks born July 1, 1985, to June 30, 1986, as well as a socioeconomically matched full-term control group were

observed prospectively for 2 years to determine the mci

dence of rehospitalization for respiratory illness. Pen natal and seasonal factors associated with increased risk for such hospitalizations were also examined. Forty-seven (36%) preterm infants were rehospitalized compared with 3 (2.5%) of 121 term infants (P < .001). Pneterm infants with and without rehospitalization were similar for mean

birth weight (1104Â±329 g and 1188Â±360 g, respectively) and gestational age (28 Â±2 weeks for both groups); however, infants who were subsequently rehospitalized

had required more days of mechanical ventilation, supple mental oxygen therapy, and neonatal intensive care. While a history of bronchopulmonany dysplasia was a risk factor for rehospitalization (45% compared with 25% of those without bronchopulmonary dysplasia, P < .05), preterm infants with no history of bronchopulmonary dysplasia still showed a 10-fold increase compared with

control infants. Among the 43 infants who required no

mechanical ventilation beyond the day of birth, 10 (23%) required rehospitalization. More than 80% of rehospital

ized infants required their first admission within 4

months of discharge from the neonatal intensive cane unit. Consequently, initial hospital discharge between September and December (the months immediately pre ceding peak respiratory viral season) resulted in an al most 3-fold increased risk of rehospitalization compared with discharge between May and August (P < .05). At 6 months of age, infants rehospitalized prior to that time had more than twice the incidence of neurologic abnor malities (12/23 [36%] vs 9/83 [11%], P < .01) than did infants who were never rehospitalized. The former group also had significantly lower motor scores on the Bayley Scales of Infant Development (89 Â±18 vs 97 Â±14, P < .05). These differences were not apparent at 15 and 24 months of age. Respiratory illness contributes signifi cantly to postdischarge morbidity in preterm infants with

Received for publication Jul 5, 1990; accepted Oct 12, 1990. Reprint requests to (C.K.C.) Dept of Pediatrics, SUNY Health Science Center, 750 E Adams St, Syracuse, NY 13210. PEDIATRICS (ISSN 0031 4005). Copyright Â©1991 by the American Academy of Pediatrics.

PEDIATRICSVol. 88 No. 3 September1991

527

Rehospitalizationfor RespiratoryIllness in

Infants of Less Than 32 Weeks' Gestation

Coleen K. Cunningham, MD; Julia A. McMiIIan, MD;

and Steven J.Gross, MD

Fromthe Departmentof Pediatrics,StateUniversityof New York HealthScienceCenterat Syracuse

MATERIALSAND METHODS

The study population included all 133 survivors

from the 156 infants of gestational age less than 32

weeks cared for in the NICU at Crouse Irving

at Viet Nam:AAP Sponsored on September 1, 2020

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Memorial Hospital between July 1, 1985, and June 30, 1986. This is the sole tertiary care facility serv ing an 18-county region in central New York State. Gestational age for these infants was determined from maternal dates of the last menstrual period. Gestational age was substantiated by early second trimester ultrasonographic examination in 85% of the cases. Gestational age of all infants of >28 weeks' gestation was confirmed by Dubowitz ex

amination.7 Twenty-one infants were transported

from outlying hospitals and 112 were inborn. Forty seven (36%) of the infants were of @27weeks gestational age and 48 (37%) had birth weights

@1ooo

g.Duringtheneonatalperiod,datacollected

prospectively included durations of mechanical ventilation, supplemental oxygen therapy, and in tensive care as well as month of hospital discharge. Bronchopulmonary dysplasia was defined as an oxygen requirement greater than room air at 28 days of life.

A control group consisted of 121 healthy, appro

priately grown, term infants matched to the pre

term infants for sex, race, and maternal age (by groups 17, 18 through 34, or 35 years), education (less than high school or completion ofhigh school), and marital status. These infants were born in the same hospital (Crouse Irving Memorial Hospital) that houses the NICU and over the same time period as were the preterm infants.

All preterm and term infants were seen for fol

low-up visits at 6, 15, and 24 months of age (using

age corrected for prematurity). At each visit infor

mation was obtained regarding all interval hospi

talizations. Charts for all rehospitalizations were

reviewedby one of us (C.K.C.). For eachhospital

admission, the infant's age, month of the year, diagnosis, treatment, and duration were recorded. All hospital admissions for respiratory illness (tach

ypnea, retractions, cyanosis) were included in the

analyses. Infants with uncomplicated otitis media or apnea were not included in this category. Infants with chronic lung disease who experienced wors ening respiratory symptoms leading to rehospitali

zation wereincluded.

To determinethe association

betweenrehospi

talization and neurodevelopmental outcome, at

eachfollow-up visit physical,neuromotor,8and de

velopmental examinations were performed. A child was considered to have abnormal neurologic ex amination results if there was evidence of moderate to severe alteration in muscle tone or hydrocephalus requiring shunt placement. Growth measurements were plotted on standard growth charts.9 Develop mental evaluations were made using the Bayley Scales of Infant Development.'0 This study was approved by the Hospital's Human Research Re

view Committee. Parental consent was obtained for each patient.

STATISTICS

Term and preterm infants were compared for rate of hospital admission. Preterm infants with and without rehospitalization were compared to

determine perinatal and demographic factors asso

ciatedwith hospitalreadmission.

Analysesof con

tinuous data were done using Student's t test and

categorical

datawereanalyzedusingx2andFisher's

exact probability tests where appropriate. All values are expressed as mean Â±SD unless otherwise noted. A P value of less than .05 was considered signifi cant.

RESULTS

Of the 133 preterm infants discharged from the nursery, 3 subsequently died of nonrespiratory causes (biliary atresia, sudden infant death syn

drome, and gastroenteritis) and were excluded from

further analysis. Four additional children died of respiratory illness during the study (data included in analysis). All 126 surviving infants returned for follow-up examination at 6 months. Two infants

did not return for follow-upat 15 months;these

two and one additional child did not return at 24 months.The parents of the 3 infants not returning for follow-up were contacted by telephone and in cidences of hospitalization were obtained. Among the full-term control infants, 118 (98%) of 121 were seen for all three follow-up visits.

Rehospitalization for any cause was required for 68 (52%) of the 130 preterm infants. Two thirds of rehospitalized infants required one or more admis sions for respiratory illness. The rate of rehospital ization for respiratory illness for preterm infants (47/130, 36%) was significantly greater than that for the term infants studied (3/121, 2.5%) (P < .001). Approximately half the admissions were to the Pediatric Service of SUNY Health Science Cen ter at Syracuse; the remaining admissions were to

regionalhospitalsthroughoutupstateNewYork.

Characteristics

of PretermInfantsWhoRequired

Rehospitalization

The 47 preterm infants who required readmission for respiratory illness were similar with regard to gestationalageandbirth weightto the 83 who never required rehospitalization (Table 1). Maternal so

(3)

Clinical CharacteristicsRehospitalized

(n=47)Not

Rehospitalized (n=83)Gestational

age, wk (mean Â±SD)28 Â±228 Â±

2Birth

wt, g (mean Â±SD)1104 Â±3291188 Â±

360Duration

of mechanical ventilation, d (mean Â±SD)29 Â±3016 Â± 24tBronchopulmonary

dysplasia, no. (%)33 (70)41 (49)1Duration

of NICU* stay, d (mean Â±SD)81 Â±5462 Â±

30@Home

oxygen, no. (%)13 (28)12 (15)

TABLE 1. Perinata.lCharacteristicsof PretermInfantsStudied

* Neonatal intensive care unit. tP< .01.

:1:P < .05.

ned), and race (80% and 90% white). The sample size may not be large enough to detect small differ ences in these socioeconomic parameters. Infants with subsequent rehospitalizations did have signif icantly greater respiratory morbidity during the newborn period, including almost twice the dura tion of mechanical ventilation and a significant increase in the incidence of BPD. More than half the infants discharged to home with oxygen (13/25, 52%) required rehospitalization (Table 1).

The 47 rehospitalized infants required 106 hos pital admissions during the first 2 years of life; 12 infants were hospitalized three or more times. The mean age of infants at the time of initial rehospi talization was 4.0 Â±4.8 months. Eighty-seven per cent of initial hospitalizations occurred prior to 1 year of chronologic age. The average length of stay for each hospitalization was 10 Â±14 days; the total number of days that infants remained in the hos pital over the first 2 years of life averaged 23 Â±40.

Infants with BPD had a greater incidence of hospital admission than those without chronic lung disease (33/74 [45%] vs 14/56 [25%], respectively,

P < .05). Those with BPD were more likely to have

multiple readmissions (26% vs 5%, P < .01) and a prolonged cumulatjve hospital stay of 30 days

(12% vs 0%, P < .01). A previous history of BPD

did not, however, influence the level of respiratory care and mortality during rehospitalization. Infants with and without BPD were equally likely to require

supplementaloxygen (23/33 [70%] vs 12/14

[86%], respectively) and mechanical ventilation (8/ 33 [24%] vs 4/14 [29%]) during acute respiratory illness. Three infants with BPD (9%) and one in fant without BPD (7%) died during rehospitaliza tion.

Despitethe importanteffectsof BPD on subse

quent respiratory morbidity, it is important to note that the incidence of rehospitalization was signifi cantly increased as a result of prematurity per se. Twenty-five percent of preterm infants without BPD required rehospitalizationâ€”a 10-fold increase

over socioeconomically matched full-term infants.

Furthermore,of the preterminfantswhorequired

no mechanical ventilation beyond the day of birth, 10 (23%) of 43 required rehospitalization (Table 2).

SeasonalPatternof Hospitalization

In addition to the severity of lung disease, the risk of rehospitalization was correlated with season

of NICU discharge and the interval between NICU

discharge and the first winter season. Fifty-five (52%) of the 106 hospital admissions occurred dur ing the 4-month period between January and April (Fig. 1). This was the period during which respira tory syncytial virus (RSV) was prevalent in the

communities; 15 of the 19 documented RSV infec tions in our population occurred during these months (Fig. 1). Rehospitalization was also more

likely to occur shortly after NICU discharge.

Thirty-eight (81%) ofthe 47 rehospitalized children required their first hospital admission within 4 months of NICU discharge. Consequently, those infants most likely to require rehospitalization dur ing their first 4 months were those discharged be tween September and December (the months im mediately preceding their first RSV season). Sev

enteen (41%) of these 42 infants required early

rehospitalization in contrast to 6 (15%) of 39 in fants discharged from the NICU from May through

August (P < .05) (Fig. 2). The group discharged

January through April had an intermediate risk of rehospitalization (31%), as infants in this group who were discharged in January had a rehospitali zation rate similar to the September through De

cembergroup(42%)while infants dischargedin the

later months were less likely to require rehospital

ization (27%). In addition, the infants discharged

during the summer months (May through August) who escaped early rehospitalization were therefore

more than 5 months of age during their first winter

at home. None of these infants required hospitali

zation during January through April of that first

year of life. Therefore, season of discharge and age

duringsubsequent

winterrespiratoryviral seasons

ARTICLES 529

(4)

TABLE 2. Duration of Ventilation Required for All Infants

Rehospitalizationand

Those RequiringDuration

of Mechanical VentilationTotal

No. of InfantsMean

Gesta tional Age, wk*No.

(%) of Infants With Rehospitali zation(s)@24

h 1â€”7d 7â€”28d >28 d43

21 25 4129.7

29.4 27.9 26.310

(23) 7 (33) 10(40) 20 (49)

* Mean gestational age of infants rehospitalized was not significantly different from that

of infants without rehospitalizations.

[11%], P < .01) at 6 months of age. This was reflected in significantly lower motor indices on the

Bayley Scalesof Infant Development.These differ enceswere no longer apparent at subsequentages

(Table 3). Infants rehospitalized prior to 6 months

and those never rehospitalized were similar with regard to growth, neurologic abnormalities, and

performance on the Bayley Mental and Motor

scalesat both 15 and 24 months of age.

DISCUSSION

We found that the high incidence of rehospitali

zation for respiratory illness among preterm infants of <32 weeks' gestation was not limited to infants

with chronic lung disease. While 45% of infants with BPD were rehospitalized, 25% of infants with

out BPD required hospital admission. The rate for this latter group was 10-fold greater than that of a matched control group of term infants.

A high rate of rehospitalization for infants with BPD has been documented previously; however, the

percentage of patients requiring repeated hospital ization has varied greatly from study to study. Investigators have found rehospitalization rates

rangingfrom 40% to 86%.46h112These ratesare not

inconsistent with our finding of 45%. The variabil ity of findings in this regard may be attributed to

inconsistencyin studydesign,especiallyin the def

inition of BPD used by various investigators. In

addition, the duration of follow-up ranged from 4

months to 2 years. It is clear, however, that preterm infants with chronic lung disease are likely to re

quire rehospitalization early in life.

Although it has been reported that preterm in fants without residual lung disease have no greater

risk of serious respiratory illness than do term infants, those studies evaluated infants born prior to i971.@'@'@ These earlier studies evaluating mor bidity among respiratory distress syndrome survi

vorsweredoneusinga patient populationwith very low survival ratesâ€”only 18% of all preterm infants who required ventilatory support survived the mi

tial hospitalization in one series.13 Therefore, these

U ALLADMISSIONS

U RESPIRATORYSYNCYTIALVIRUSISOLATED

o@4

-J

@ @- ,_ > 0 Z

@

@ >.

@

U)

@ a. 8 0 LU (

-) w

Month

Fig 1. Numberof rehospitalizationsfor respiratoryill

ness for preterm infants by month.

50

(I) C

F

sept-doc Jan.*pr may-aug

month of NICU discharge

Fig2. Rehospitalizationfor respiratoryillnesswithin4

months of neonatal intensive care unit (NICU) discharge: relationship to month of discharge.

@ J@< .05, infants

discharged September through December were more

likely to require early readmission than those discharged May through August.

had profound impacts on incidence of rehospitali

zation.

Neurodevelopmental Follow-up

The 33 preterm infants who required rehospital ization(s) for respiratory illness prior to their first developmental follow-up assessment at 6 months

of age were compared with the 83 infants who required no such hospital admission during their first 2 years of life. The infants who required early

hospitalization had more than twice the incidence of neurologic abnormality (12/33 [36%] vs 9/83

ii

2O@

10

4O@

3O@

2O@

(5)

TABLE3. NeurodevelopmentalOutcomeof I

Never Rehospitalized*nfants

Requiring Early Rehospitalization ComparedWith InfantsEvaluation

at 6 moEvaluation at 15 moEvaluation at 24 moRehospitalizedNotRehospitalizedNotRehospitalizedNot(n

= 33)Rehospitalized (n=83)(n

= 33)Rehospitalized (n=81)(n

= 32)Rehospitalized (n=81)

10 (30)15(25)9 (18)5 (15)12 (15)7 (22)20

(27)14 (17)7 (21)15 (19)7 (22)18

(22)3

(9)7 (8)4 (12)10 (12)7 (22)15 (19)

Length <5 percentile, no. (%)

Weight <5 percentile, no. (%)

Head circumference <5 percentile,

no. (%)

Bayley MDI (mean Â±SD) 97 Â±21 101 Â±17 99 Â±21 97 Â±20 92 Â±23 94 Â±20

Bayley PD! (mean Â±SD) 89 Â±18t 97 Â±14t 92 Â±24 99 Â±20 85 Â±22 89 Â±16

Neurologic abnormality, no. (%) 12 (36)@ 9 (11)@ 7 (21) 9 (11) 6 (19) 6(7)

* The 10 infants first rehospitalized after 6 months of age, as well as the 4 infants who died of respiratory illness, were

not included in this comparison. MDI, Mental Developmental Index; PD!, Psychomotor Developmental Index.

t P < .05.

:I:P< .01.

infants cannot be considered to be representative

of infants who now leave the nursery alive.

More recent investigators have studied infants without chronic lung disease and found readmission

for respiratory illness required for 11% to 33% of patients.â€•6â€•5 There is, however, considerable var

iability in infant selectionfor study. Factors that are likely to alter the risk of rehospitalization in dude the gestational age of infants included and the overall survival of the cohort. Additionally, if only infants with severe residual lung disease are

definedas havingBPD, then the groupwithout

BPD will include many infants with mild to mod erate symptoms, in whom respiratory morbidity is more likely to develop. Within the population in

cludedin ourstudy,thegestational

ageoftheinfant

was itself not a risk factor for readmission. It seems

likely, however,that infants of 32 to 36 weeks'

gestation and those of 36 to 40 weeks' gestation have different rates of rehospitalization than the infants studied. Results of studies that include pa

tients of more advanced gestational ages cannot be

assumed to apply to the very preterm infants. In creasing rates of rehospitalization for respiratory illnessaccompanyingincreasingsurvivalof preterm infants hasbeenshownpreviouslyby Mutch et al'6 in a study comparing very low birth weight (VLBW;

s1500 g) infants born between 1968 and 1972 with a similar cohort born between 1974 and 1978. As survival increased from 35% to 48%, rates of rehos pitalization for respiratory infections increased from 9.8% to 15.5%. In the present study, survival was 85% and rehospitalization rates for respiratory

illness showed a corresponding increase to 36%

overall.

An increased frequency of respiratory viral infec tion during the winter months is expected among pediatric patients. Full-term healthy children born

duringthe 6 monthsprior to and includingthe

month of peak RSV infection have been shown to be more likely to require hospitalization than those infants born during the remainder of the year.'7 To our knowledge, a seasonal pattern has not been shown previously among preterm infants. We have found that infants discharged shortly before the

peak respiratory viral seasonare most likely to

require early rehospitalization. It is likely that pre

term infants are at greater risk soon after hospital

discharge secondary to many factors including

smallsize,residualpulmonaryabnormalities,

and

lower amounts of maternal IgG transferred trans placentally.

At the time of NICU discharge, parents are often counseled concerning the means by which the need for repeated hospitalization may be avoided. Ex

posureto tobaccosmoke,to individuals with viral

illness, and to crowds is discouraged, and breast

feedingmaybeadvocated.Unfortunately,datawere

not available regarding these and other important confounding variables including family history of allergies, exposure to day care, and presence of other children in the household. Nevertheless, the

increasedrisk for rehospitalization

amongthose

infants discharged from the NICU during the fall

months,asdemonstrated

in thisstudy,shouldbea

persuasive

argumentto emphasize

the importance

of protecting these infants in particular.

The severity of illness documented in our pa tients who were admitted demonstrates that con cern among practitioners about the potential seri ousness of respiratory illness in preterm infants is

justified.The majorityof the admissions

seenin

this study were for significant respiratory illness.

Seventy-fivepercentof all infantsrehospitalized

requiredinitiationof oxygentherapyand 26% of

those admitted required mechanical ventilation

duringoneor morehospitalizations.

ARTICLES 531

(6)

Few investigators have examined the relationship

between rehospitalization in infants and their neu

rodevelopmental outcome. McCormick et al'5 re ported that among 95 VLBW infants who were

rehospitalized

for any reasonduringthe first year

of life,53 (56%)hadmoderateto severecongenital

anomaliesor developmental

delayat 12monthsof

age. In contrast, among 164 VLBW infants born

duringthe sameyearwhodid not requirerehospi

talization,only 40 (25%) had a pooroutcome.In

that study 47% were hospitalized for respiratory

problems.Furthermore,nearly20% of the rehos

pitalizationswereas a consequence

of congenital

abnormalitiesor developmental

delay,whichcon

foundsthe relationshipwith developmental

out

come. Hack et al' found that among a cohort of 90 VLBW infants born in 1977, 30 required rehospi

talization(s) during their first year of life. Neuro

developmental outcome at 8 and 20 months of age was similar for nonhospitalized infants and those

hospitalizedfor acuteillnessincludinguncompli

catedrespiratoryinfections.Pooreroutcomewas

found only in a small subgroup of VLBW infants

rehospitalized for chronic complications of prema turity. We have demonstrated that although there

are greater numbers of neurologic abnormalities

and lower standardized test scores at 6 months

amonginfants rehospitalizedfor respiratoryillness

prior to that time, there is no measurable difference

in neurodevelopmental

outcomeby 15 monthsof

age. The finding at 6 months may be a reflection of the prolonged neonatal course among infants re

quiring early rehospitalization rather than of the

readmissionitself.

IMPLICATIONS

Rehospitalization for respiratory illness contrib utes significantly to the morbidity and mortality associated with prematurity. As the care and sur vival of preterm infants change, the morbidity among survivors needs periodic reevaluation. It is

clear from this study that even preterm infants

without neonatal lung disease are at significant risk for serious respiratory illness requiring rehospital ization over the first 2 years of life and would

potentially benefit from strategiesto prevent RSV

and other respiratory infections.

We thank Michele M. Choyke for secretarial assist ance.

REFERENCES

1. Hack M, DeMonterice D, Merkatz IR, Jones P, Fanaroff A. Rehospitalization ofthe very-low-birth-weight infant: a con tinuum of perinatal and environmental morbidity. AJDC. 1981;135:263â€”266

2. Meyers MG, McGuiness GA, Olson DB, et a!. Respiratory illnesses in survivors of infant respiratory disease syndrome. Am Rev Respir Dis. 1986;133:1011â€”1018

3. Outerbridge EW, Nogrady MB, Beaudry PH, Stern L. Idi opathic respiratory distress syndrome: recurrent respiratory illness in survivors. AJDC. 1972;123:99â€”104

4. Groothuis JR, Gutierrez KM, Lauer BA. Respiratory syn cytial virus infection in children with bronchopulmonary dysplasia. Pediatrics. 1988;82:199â€”203

5. Sauve RS, McMillan DD, Young L, et al. Home oxygen therapy: outcome of infants discharged from NICU on con tinuous treatment. Clin Pediatr (Phila). 1989;28:113â€”118 6. Sauve RS, Singhal N. Long-term morbidity of infants with

bronchopulmonary dysplasia. Pediatrics. 1985;76:725â€”733 7. Dubowitz LMS, Dubowitz V, Goldberg C. Clinical assess

ment of gestational age in the newborn infant. J Pediatr. 1970;77:1â€”10

8. Ellison PH, Horn JL, Brouning CA. Construction of an

infant neurological international battery (INFANIB) for the assessment of neurological integrity in infancy. Phys Ther. 1985;65:1326â€”1331

9. Growth charts 1976. Monthly Vital Statistics Report. Wash ington, DC: National Center for Health Statistics; Health Resources Administration; 1976;25(3) suppl (HRA) 75â€”1120 10. Bayley N. Bayley Scales of Infant Development. New York,

NY: Psychological Corp; 1969;1-78

11. Morgan MEl. Late morbidity of very low birthweight in fants.Br Med J. 1985;291:171â€”173

12. Yu VY, Orgill AA, Astbury J, et al. Growth and development of very low birthweight infants recovering from broncho pulmonary dysplasia. Arch Dis Child. 1983;58:791â€”794 13. Harrod JR, Heuruex P, Wanginsken OD, Hient CE. Long

term follow-up of severe respiratory distress syndrome treated with IPPB. J Pediatr. 1974;82:277â€”286

14. Lamarre A, Linsao L, Reilly BJ, Swyer PR, Levison H. Residual pulmonary abnormalities in survivors of idiopathic respiratory distress syndrome. Am Rev Respir Drs. 1973; 108:56-61

15. McCormick MC, Shapiro S, Starfield BH. Rehospitalization in the first year of life for high-risk survivors. Pediatrics. 1980;66:991-999

16. Mutch L, Newdick M, Lodwick A, Chalmers I. Secular changes in rehospitalization ofvery low birth weight infants. Pediatrics.1986;78:164â€”171

17. Glezen WP, Paredes A, Frank AL, et al. Risk of respiratory syncytial virus infection for infants from low-income fami lies in relationship to age, sex, ethnic group, and maternal antibody level. J Pediatr. 1981;98:708â€”715

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1991;88;527

Pediatrics

Coleen K. Cunningham, Julia A. McMillan and Steven J. Gross

Rehospitalization for Respiratory Illness in Infants of Less Than 32 Weeks' Gestation

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Coleen K. Cunningham, Julia A. McMillan and Steven J. Gross

Rehospitalization for Respiratory Illness in Infants of Less Than 32 Weeks' Gestation

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