Materials and methods

          This was a one-year prospective cohort study of children attending our day-care between August 2003 and October 2004.  We excluded children with any congenital anomalies or immunodeficiency.  The study was reviewed and approved by The Khon Kaen University Ethics Committee for Human Research and only children with informed, written parental consent were enrolled.  Every child had a personal daily one-year record comprising:  (1) personal history (viz., history of birth, age, sex, family members, feeding history, family’s pets, duration of day-care attendance); (2) daily record of respiratory infection symptoms (i.e., fever, nasal discharge, cough, ear discharge); and, (3) antibiotic treatment.  Day-care workers and parents recorded all data.  Every 2-4 weeks, the investigators checked all records for any missing data.  The history of all of the illnesses was checked against the hospital records at Srinagarind Hospital, Khon Kaen University, Thailand.

          A common cold or simple URI was defined as ‘the presence of nasal discharge, cough with or without fever which resolved within 2 weeks’⁷. Symptoms that lasted more than 14 days were defined as suspected of ‘sinusitis’⁷. Otitis media was labeled only in the child who was diagnosed by a doctor shown in the hospital records. An illness was counted as a new episode when the symptoms occurred at least 3 days after the resolution of the previous episode.

Statistical analysis

          Descriptive statistics were used as the baseline data.  The Chi square and Fisher’s exact tests were used for comparisons as appropriate (p<0.05).  Logistic regression and multivariate analysis were used for risk factors analyses.

Results

          Our day-care center raises children age between 6 months to 4 years, separates into 3 levels; level 1 aged under 2 years, level 2 aged between 2-3 years and level 3 aged over 3 years. Each level, the children are raised in the rooms with mean space around 2 square meter/child. The ratios of baby sister to children are 1: 4-5, 1: 8-9 and 1: 12-14 in the level 1, 2 and 3 respectively. During study period, 138 children were attending the day-care and of those 90 (65%) were enrolled, including 47 males (52.2%).  The children were between 8 and 53 months of age (mean 20±9.6 months). Sixty percent of all the children received a 4-month period of exclusive breastfeeding.  Atopic history among the parents was found (38%), while 29% of all children were passive smokers.  The mean duration of day-care attendance before enrolment was 11±9.2 months (Table 1).

Table 1 Baseline demographic data of the children

          During the study period, every child suffered at least one cold.  A total of 1,100 colds was counted.  The incidence was 3 to 25 colds/child/year (mean, 12±5.4; median, 12).  The duration of each cold was 1 to 26 days (mean 5±1.9; median, 4).  Incidence peaked in the cool season between November and February.

          Only one episode of otitis media was found (0.1%); however, 131 episodes (11.9%) of sinusitis were suspected in 41 children (45.6%). No other complications were found.  There were 57 episodes (5.9%) of antibiotics (mostly amoxicillin) being inappropriately prescribed for simple common cold. Of the 131 episodes of sinusitis, antibiotics were prescribed for only 13 episodes, while the remaining 118 episodes were self-limiting, perhaps because they were caused by viral infections or were the result of allergic rhinitis symptoms.

          Although every child suffered from a cold in the one-year period, the primary risk factor for frequent colds (i.e., over 8 colds/year) was ‘attending day-care before being 2 years of age (odds ratio of 11; 95%confidence interval, 1.4-89.7; p = 0.02).  All of the other risk factors, such as allergy, pets and number of children per family, passive smoking, and duration of day-care attendance, were not statistically significant (Table 2).

Table 2          Risk factors of frequent colds/year*

Discussion

          This study demonstrated that every child attending our day-care experienced at least one cold episode each year, while 76.7% of them had more than 8 colds/year.  The incidence was 12±5.4 colds/child/year.  The mean duration of each cold was 5±1.9 days. Otitis media and sinusitis were found in 0.1% and 11.9%, respectively.  Children who attended day-care before their 2^nd birthday had the greatest risk of getting frequent colds (more than 8 colds/year) than the older children in the study.

The incidence of getting a cold in this study was similar to previous studies but the incidence of complications, such as otitis media and sinusitis, was different.^7-9  Our study found otitis media in only 1% of participants compared to the 17-32% found in other studies, perhaps because the definition of otitis media used in our study required a doctor's diagnosis.  Moreover, although daily records concerning respiratory symptoms were obtained, no attempt was made to get an ear examination for all of the children with colds; therefore, some children who developed mild ear symptoms might have been missed and/or might have had spontaneous resolution without any treatment, resulting in the lower incidence.

We found 11.9% of children had respiratory symptoms which lasted more than 14 days and defined this as sinusitis.  This figure is similar to previous studies, where 5 to 13% of children who suffered from viral upper respiratory tract infection might be complicated by secondary bacterial infection of paranasal sinuses.^7,10-11  This high incidence, however, was due to:  (1) a diagnosis using clinical symptoms such as prolonged nasal discharge of more than 14 days without physical examination or other definitive confirmations; even though (2) such symptoms might be difficult to distinguish from allergic rhinitis.  Interestingly, although 60% of all of the children in our study had 4 months of exclusively breastfeeding, 38% had parental atopic history that might have caused a high incidence of allergy in these children.

Our study confirmed the finding in previous studies regarding the duration of the simple common cold of no longer than 7 days.⁷ Most colds were self-limiting and the incidence of antibiotic overuse quite low (5.9%) compared to the 23.6% reported by the Thai Ministry of Public Health¹² and the 60 to 71% reported elsewhere.^13-14  Most of the parents of the children attending our day-care are healthcare workers, which may account for the lower incidence of antibiotic overuse; nonetheless, some children were still getting inappropriate antibiotic treatment, exacerbating antibiotic resistance among microorganisms.

The limitation of this study were 1) the results came from the daily personal records which might have some missing data, and 2) all the children did not underwent physical examinations for the definite diagnosis.

          The two critical factors involved in the transmission and development of infectious diseases in the day-care are the hosts (personal immunologic factors) and environmental factors (personal hygiene and the potential for sharing respiratory secretions).¹⁵ The significant risk factor we found for frequent colds (i.e., >8 colds/year) in this study was ‘attending day-care by children under 2 years of age’.  The other factors such as allergy, pets and number of child per family, passive smoking, and duration of day-care attendance had no statistical significance. Previous studies also showed that young children attending day-care had a higher risk of recurrent ear infections,^16-17 but we only examined the host factors associated with frequent infections in order to improve the day-care.  Further study of the environmental factors should be done.