There are currently 5 coronaviruses (family Coronaviridae , genus Coronavirus ) known to infect humans: the 4 human coronaviruses (HCoVs) HKU1, NL63, 229E, and OC43, and the coronavirus responsible for severe acute respiratory syndrome (SARS-CoV). HCoVs 229E and OC43 were discovered in the 1960s.1 – 3 4 – 7 8 9 – 12 4 , 7 , 13 , 14 15 – 18 children .19 – 21
The primary objective of this study was to use prospective, population-based surveillance to compare the detection rates for HCoVs HKU1, NL63, 229E, and OC43 among children <5 years of age hospitalized for acute respiratory illness and/or fever (ARI/fever) with rates in asymptomatic control children of similar ages during 2 winter seasons in 3 geographic sites. In addition, the study compared the clinical characteristics between children hospitalized with confirmed HCoV and those hospitalized with other respiratory viruses. Finally, by combining these data with the data from 3 previous years of hospital surveillance that did not include asymptomatic control children ,22
METHODS
Study Design
ARI Surveillance in Hospitalized Children
As part of the surveillance activities of the New Vaccine Surveillance Network,23 – 25 children <5 years of age with an admission diagnosis of ARI/fever who resided in the 3 counties surrounding Rochester (New York), Nashville (Tennessee), and Cincinnati (Ohio) during the period between October 2003 and April 2005. Hospital surveillance was conducted 4 d/wk during 2003 to 2004, 7 d/wk during the months when influenza was circulating in each region between 2004 and 2005, and 3 to 4 d/wk when influenza was not circulating. Surveillance hospitals accounted for >95% of the pediatric hospitalizations in each county. ARI admission diagnoses included acute respiratory illness, apnea, asthma, bronchiolitis, croup, cystic fibrosis exacerbation, febrile neonate, febrile seizure, fever without localizing signs, hypothermia, influenza, otitis media, other respiratory infection, paroxysmal cough, pharyngitis, pneumonia, respiratory distress, human respiratory syncytial virus (RSV) infection, rule-out sepsis, sinusitis, tonsillitis, upper respiratory illness, and wheezing. Children were excluded if they had been hospitalized during the previous 4 days, were newborns hospitalized since birth, had neutropenia from chemotherapy, had a known nonrespiratory cause for the hospitalization, or had been sick for >14 days when screened; all others were eligible. The same protocol was used to carry out hospital surveillance at the Rochester and Nashville sites during the preceding 3 years.
Asymptomatic Control Enrollment
Children <5 years of age currently without ARI/fever who resided within the 3 counties were systematically enrolled as asymptomatic controls from 8 to 10 (depending on the year) large urban and suburban outpatient practices during 2 d/wk from December 2003 to April 2004 and October 2004 to April 2005. These children will hereafter be referred to as “controls.” Study staff prospectively identified eligible control children by reviewing clinic visit logs for well-child visits and spoke to the parent/guardian to determine that the child did not currently have ARI symptoms (ie, chief complaints of a respiratory illness including fever, cough, earache, nasal congestion/runny nose, shortness of breath/rapid or shallow breathing, sore throat, vomiting after cough, or wheezing). In addition, the parent or guardian of each control child was asked to report the most recent previous medical visit for fever or respiratory symptoms during the surveillance period. Of the enrolled control children , 4.5% were excluded from analysis because review of the clinical records indicated the child had signs of ARI during their visit, as noted by the clinician who conducted their physical examination. There was no follow-up to determine whether subjects became ill or not soon after their enrollment visit.
Data Collection
For all enrolled hospitalized and control children , study staff obtained clinical and epidemiologic data from parent/guardian interviews and medical records using standardized methods and collected combined nasal/throat swab specimens. Preexisting high-risk conditions among enrolled children were identified based on the Advisory Committee on Immunization Practices recommendations for influenza vaccination and included history of asthma, heart disease, sickle cell anemia, cystic fibrosis, diabetes mellitus, or neuromuscular conditions, such as seizures, cerebral palsy, or muscular dystrophy.26
The study was approved by the institutional review boards of each site and the Centers for Disease Control and Prevention. Informed consent was obtained from each parent/guardian before enrollment.
Research Laboratory Methods
Nasal/throat specimens were tested for HCoV using real-time reverse-transcription polymerase chain reaction (RT-PCR) assays for HCoVs HKU1, NL63, 229E, and OC43.19 , 22
Data Analysis
Analyses comparing HCoV infections among hospitalized children and controls and assessing clinical factors among hospitalized children were restricted to the 5- and 7-month periods when both cases and controls were enrolled (December 2003 to April 2004 and October 2004 to April 2005). Repeat hospitalizations/visits occurring among cases and controls were not excluded or adjusted for in the analysis. There were 8 children with a second hospitalization or visits within 30 days of the first, and none of the children were positive for HCoV on both occasions. Categorical data were assessed with Pearson χ2 and Fisher exact tests. The medians and interquartile ranges were calculated for continuous variables. SAS version 9.2 was used for all analyses (SAS Institute, Cary NC), and a 2-sided 0.05 significance level was applied for all statistical tests performed.
Comparison of HCoV Detections Between Hospitalized and Control Children
Crude unadjusted odds ratios and 95% confidence intervals were calculated using logistic regression. Five conditional logistic regression models were also fit. One model estimated the adjusted odds (aOR) of HCoV detection among hospitalized children versus controls while controlling for age-group (0–5, 6–11, 12–23, 24–59 months), county, and month of hospitalization/visit. Four analogous models were fit to assess each HCoV species separately. Differences between cases and controls were assessed both including and excluding the hospitalized HCoV cases coinfected with IV, RSV, HPIV, or HMPV, and the results were similar.
Clinical Outcomes Among Hospitalized Children
To assess the severity of HCoV infections relative to other respiratory viruses, the hospitalized children were divided into 3 subgroups for comparison: (1) HCoV positive (HCoV+) children who were not coinfected with IV, RSV, HPIV, or HMPV; (2) HCoV+ children who were coinfected with either IV, RSV, HPIV, or HMPV; and (3) HCoV negative (HCoV−) children who were infected with IV, RSV, HPIV, or HMPV.
Overall Prevalence and Seasonality of HCoV From 2000 to 2005
Hospital-based surveillance for ARI/fever among children <5 years of age had been conducted during the previous 3 years by the Rochester and Nashville sites using the same study protocols and testing methods (without enrolling healthy controls). The prevalence (1.8%) and clinical features of the 19 HCoV+ children hospitalized from October 2001 to September 2003 have been previously reported.22
RESULTS
HCoV Among Hospitalized Children
During the 12 months from December 2003 to April 2004 and October 2004 to April 2005, 1610 (82%) of 1952 children hospitalized for ARI/fever were enrolled in the study; test results were available for one or more of the 4 HCoV species in 1481 (92%) of these children . Of these, 113 (7.6%) tested positive for HCoV. Among the species, OC43 was the most frequent, with 58 (3.9%) detections, followed by 26 (1.8%) NL63, 17 (1.1%) HKU1, and 15 (1.0%) 229E (Table 1 ). Three cases were infected with more than one strain of HCoV: 2 with both HKU1 and OC43 and 1 with both NL63 and 229E.
Table 1: Number and Percent Testing Positive for HCoVs Among ARI/Fever Hospitalizations and Asymptomatic Controls During the 12 Months When Controls Were Enrolled, December 2003 to April 2004 and October 2004 to April 2005
Other Viral Infections Among Hospitalized Children
Coinfections were identified in the 113 hospitalized children with HCoV infection: 7 (6%) also tested positive for IV, 17 (15%) for RSV, 1 (1%) for HPIV1–3, 6 (6%) for HMPV, 8 (7%) for human rhinovirus, and 3 (3%) for human bocavirus. Rates of coinfection for the 4 HCoV species were as follows: 59% for HKU1, 40% for 229E, 36% for OC43, and 23% for NL63 (not statistically significantly different). Only 1 HCoV+ child was coinfected with 2 other respiratory viruses (IV and RSV). Overall, 41 children (36%) had a viral coinfection, and 30 of the coinfections were with viruses known to be associated with serious ARI (IV, RSV, HPIV, and HMPV). After excluding these 30 cases, the proportion of hospitalized children with HCoV infection was 5.7%. Of the 496 hospitalized children who were HCoV negative but were infected with a virus associated with serious ARI (subgroup 3), 145 (29%) tested positive for IV, 276 (56%) for RSV, 29 (6%) for HPIV1–3, and 72 (15%) for HMPV.
HCoV Among Control Children
During the same 2 study periods described earlier in the text, 822 (89%) of 919 asymptomatic controls were enrolled, and test results were reported for HCoV in 742 (90%) (Table 1 ). Of these 742 controls, 53 (7.1%) tested positive for HCoV. The most common species was OC43, with 20 detections (2.7%), followed by 18 (2.4%) NL63, 12 (1.6%) HKU1, and 3 (0.4%) 229E.
Comparison of HCoV Detections Between Hospitalized and Control Children
When compared with the controls, with or without excluding coinfections, significantly higher detection rates were not observed among hospitalized cases for any HCoV or for any of the specific HCoV species (Table 1 ).
Demographic Characteristics of Hospitalized and Control Children
Among the hospitalized and control groups, respectively, no significant differences existed in the demographic characteristics between those with and without HCoV infection (Table 2 ). More than half (52%) of the HCoV+ hospitalized children were <6 months of age, whereas HCoV infection among controls was more evenly distributed between the age-groups (P = 0.001). However, the proportion of children with HCoV infection was not significantly different in any age-group for hospitalized children when compared with controls (Table 3 ). Among those <6 months of age, the difference was greater but still did not reach statistical significance when coinfected cases were included (8.1% vs. 4.8%, P = 0.09).
Table 2: Demographic Characteristics of Children Hospitalized for ARI/Fever (Excluding Those Coinfected With IV, RSV, HPIV, and HMPV) and Asymptomatic Controls With and Without HCoV During the 12 Months When Controls Were Enrolled
Table 3: Age-specific HCoV Detection Rates (%) Among ARI Hospitalizations and Asymptomatic Controls During the 12 Months When Controls Were Enrolled
Medical History of Hospitalized and Control Children
The medical history and selected characteristics for hospitalized children and controls positive for HCoV overall and for each HCoV species are shown in Table, Supplemental Digital Content 1, https://links.lww.com/INF/B7 children infected with species NL63, preexisting high-risk conditions were more common among hospitalized children than controls (33% vs. 0%, P = 0.01). However, in both groups, the prevalence of high-risk conditions did not differ between NL63-positive and NL63-negative children . The results were the same when the cases coinfected with IV, RSV, HPIV, or HMPV were included, and no other significant differences were found between HCoV+ hospitalized children compared with HCoV+ controls. Statistical comparisons were not made between cases and controls for species HKU1 and 229E because of the small numbers in each group.
Adjusted Model Comparing HCoV Detections Between Hospitalized and Control Children
Infection with any HCoV or with a specific HCoV species was not associated with hospitalization in models controlling for age, county, and month of hospitalization/visit and excluding hospitalized children who were coinfected with other respiratory viruses. The aORs (confidence intervals) of HCoV detection among hospitalized children versus controls were as follows: for all HCoV infections, 0.79 (0.53–1.17); for HKU1, 0.57 (0.23–1.44); for NL63, 0.63 (0.31–1.30); for 229E, 2.38 (0.63–9.05); and for OC43, 0.82 (0.45–1.49). The estimated crude odds ratios and aORs changed little when HCoV+ coinfected hospitalized children were included in the analyses.
Discharge Diagnosis and Severity of Disease Among Children Hospitalized With HCoV Compared With Those Hospitalized With Other Respiratory Viruses
Children infected with respiratory viruses (IV, RSV, HPIV, or HMPV) (Table 4 , subgroup 2 and 3) were more likely than children singly infected with HCoV (Table 4 , subgroup 1) to have had a discharge diagnosis of pneumonia or bronchiolitis, a hospital stay ≥3 days, or to require supplemental oxygen, although the last difference was statistically significant only for subgroup 3 versus subgroup 1. No statistically significant differences were observed between the children coinfected with HCoV plus another respiratory virus (subgroup 2) and the children infected only with another virus (subgroup 3). Coinfected children (subgroup 2) had a discharge diagnosis of otitis media more often than those singly infected with HCoV (subgroup 1). In addition, among those singly infected with HCoV, 5 of the 7 with a discharge diagnosis of croup were infected with species NL63. Croup was also more common among those singly infected with species NL63 than those infected only with a noncoronavirus respiratory virus (23.8% vs. 5.8%, P = 0.001).
Table 4: Discharge Diagnoses and Severity of Illness Among Children Hospitalized for ARI/Fever
Overall Prevalence and Seasonality of HCoV From 2000 to 2005
The prevalence of HCoV varied during the 5 study years, with a higher proportion of children with HCoV detected during 2000 to 2001 and during the 2 seasons from 2003 to 2005 that are the focus of this study (Fig., Supplemental Digital Content 2, https://links.lww.com/INF/B8 children with HCoV detected each month was very similar among both hospitalized children and controls (Fig., Supplemental Digital Content 3, https://links.lww.com/INF/B9
DISCUSSION
This is the first study that reports the frequency of the 4 recognized HCoV species among hospitalized children and asymptomatic controls in several regions of the United States during multiple years. No statistically significant increase was observed in the rates of detection for HCoV or for any of the 4 individual species of HCoV among the hospitalized cases when compared with the controls, regardless of whether the 27% of hospitalized children who were coinfected with IV, RSV, HPIV, or HMPV were excluded. The children hospitalized for ARI/fever in whom HCoV alone was detected appeared to be less severely ill than children with IV, RSV, HPIV, or HMPV infections, and the particular association observed between species NL63 and croup was consistent with other studies.27 – 29 children coinfected with HCoV and other respiratory viruses were clinically similar to those infected only with IV, RSV, HPIV, or HMPV. This suggests that the other viruses rather than HCoV were responsible for the hospitalization.
The prevalence of HCoV species appeared episodic during the 5 seasons, with 2 years of lower overall activity separating several years of higher activity. A similar episodic pattern was reported by another study.7 17
Overall, our finding of no association between HCoV infection and serious illness among hospitalized children bolsters the findings of several previous studies.19 – 21 19 children <3 years of age and asymptomatic community controls found HCoV detection rates were the same for cases and controls (4%).20 children (4.4%), and neither species was detected in a specimen taken during an ARI episode that required hospitalization.21 18
Limitations of our study include the fact that the 3 geographic areas in this study may not be representative of the rest of the United States. Also, we did not assess bacterial coinfections or antibiotic use, which could have affected the clinical outcomes for those children who were hospitalized. Our study did not collect data about respiratory symptoms before or after enrollment. Both cases and controls may have tested positive for HCoV from a very recent infection and developed symptoms after enrollment. As previous studies have noted that HCoV may be shed at least 14 days after acute infection,30 , 31 children , and few children infected with HCoV had medically attended visits for respiratory illness in the month before enrollment. Another possible limitation is that asymptomatic children were not enrolled year-round, but the peak periods of HCoV circulation were included. Finally, we did not test the controls for the additional respiratory viruses for which the hospitalized children were tested.
This large prospective, multicenter, population-based study of HCoV infections among both cases and controls during several seasons found no association between hospitalization for ARI/fever and HCoV infection. This type of study, however, cannot rule out the possibility that the infection was causal in a subset of the children . It is possible that host factors are of primary importance in responding to HCoV infections, and further study of the relevance of host or other cofactors in symptomatic illness would help move the field forward. Furthermore, as very few studies of the known HCoVs have included a robust sample size, multiple years, and a control group, more studies would be helpful to verify the findings of this study. Given the low prevalence of hospitalized HCoV cases, the frequency of viral coinfection, and the differences in yearly circulation patterns, conducting future studies with larger numbers of cases and well-matched controls will be challenging. However, new multipathogen PCR platforms may provide opportunities for future studies of respiratory disease that include HCoV. Biopsy and autopsy studies with in situ identification of HCoV and microscopic assessment of fatal cases might also help elucidate viral etiology. Studies using a variety of research strategies are needed to better delineate the role of HCoV infections among children .
ACKNOWLEDGMENTS
The authors acknowledge the contribution of the following persons to surveillance-related activities: University of Rochester: Geraldine Lofthus, Kenneth Schnabel, Andrea Marino, Christina Albertin; Vanderbilt University: Diane Kent, Amy Podsiad; Cincinnati Children 's Medical Center: Diana Henderson, Michol Holloway, Vanessa Florian, Emily Gruebe, Linda Jamison, David Witte, Joel Mortensen; CDC: Minnie Wang, Frances Walker, John Copeland, Ranee Seither, and Jennifer Reuer.
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