Skin infections in children in a New Zealand primary care setting: exploring beneath the tip of the iceberg

Skin infections are a common complaint in primary care and are usually considered benign. However, in both New Zealand (NZ) and international settings, these infections are becoming an increasingly significant source of childhood morbidity, with the rate of skin infections requiring hospitalisation (termed serious skin infections) steadily increasing during the last two decades.1-7In NZ, the rate of serious skin infections, doubled between 1990 and 2007.4 In 2004, a report by Hunt found the national rate of cellulitis in children was twice that of Australia and the United States of America.8Recent analyses have found that serious skin infections contribute heavily to health inequalities with the greatest hospitalisation rates observed in M ori and Pacific children.4,5,8-11 These trends are hypothesised to reflect corresponding patterns of disease in the community,8 however there are no published studies examining skin infections in the NZ primary care setting, where many patients initially present and the major burden of illness is managed. This deficit is likely due to the lack of routine primary care level surveillance for most health conditions in NZ.Hospital admissions for serious skin infections represent the tip of the iceberg in relation to the wider community burden of disease.4,8We aimed to estimate the incidence of skin infection cases in primary care in children in the Tairawhiti (Gisborne) region, describe the basic epidemiology of these infections, and compare these characteristics with serious skin infections hospitalised in the region during the same period.Methods We conducted a prospective observational analysis of skin infection cases in children seen by a cohort of general practitioners (GPs) in the Tairawhiti region. Study locationThe Tairawhiti region is a relatively isolated area of 45,000 people on the East Coast of NZs North Island. The region is unique for its large M ori population (47.3% of the total population and 58.4% of the 0-14 year old population), young age distribution (26.2% of people are aged less than 15 years),12 and high levels of deprivation (the Gisborne region has the highest proportion of the most deprived residents in the country).13 In Tairawhiti, childhood skin infections present a major challenge to both primary and secondary health services. The regions serious skin infection incidence is not only the highest in NZ,4 research presented in companion articles in this issue of the New Zealand Medical Journal has shown it is considerably greater than that expected, even after standardising for the high-risk age, ethnicity and deprivation population composition. General practitioner recruitment and data collectionThe raw data for this study were collected by prospective consultation coding by a group of Tairawhiti GPs. All GPs within the region were approached and their voluntary participation in this study sought. Out of the usual local GP population of approximately 20 full-time equivalent practitioners working in six primary practices, nine GPs from three different practices agreed to participate. During the study period, 4627 of the 18,456 (25.1%) 0-14 year olds usually resident population of the Tairawhiti region were registered in the practice populations of these GPs. Over the 10-week period, 19 May 2008 to 28 July 2008, GPs coded all incident cases of skin infection in children using the READ code system. Similar to International Classification of Disease (ICD) codes used in hospitals, READ codes are a standardised and hierarchically-arranged clinical terminology system widely used in primary care practices for coding diagnoses as well as a range of patient demographic and clinical data.14 All skin infections were included regardless of whether they were the primary reason for presentation or a secondary diagnosis. Repeat visits for the same episode of infection were not coded. All visits were during routine office hours of 8am to 5pm, Monday to Friday. A minimum level code of M0.00 (Skin/subcutaneous tissue infections) was recorded in the computerised clinical records of appropriate patients using MedTech32 00ae,the electronic patient management system used in all participating practices. Email reminders were sent to GPs every 3-4 weeks during the data collection phase. At the end of this period, the Query Builder 00ae function of MedTech32 00ae was used to design and run a standardised data query. An arbitrary and anonymous unique identifier was assigned to each case and raw data variables including READ code and free-text diagnosis description, date of birth, gender and ethnicity (M ori vs. non-M ori) were extracted and collated centrally. Case definitionCases of skin infection were diagnosed clinically based on the experience of participating GPs, however a written case definition was provided to standardise inclusion criteria: cAny child aged 0-14 years old, seen by a participating GP during the study period, with clinical evidence of a new episode of active bacterial infection of the skin or subcutaneous tissue including any of the following diagnoses: cellulitis, erysipelas, impetigo, subcutaneous abscess, furuncle, carbuncle, acute lymphadenitis, any pyoderma including bacterial super-infection of eczema/scabies/chickenpox/insect bites, and any other infection of the skin or subcutaneous tissue.d Hospital casesWe used anonymised hospitalisation data provided by the New Zealand Ministry of Health to identify all cases of serious skin infection in children aged 0-14 years admitted to Gisborne Hospital over the same 10-week period specified above. The case definition of hospitalised serious skin infection utilised in this study was developed in earlier work by the authors and has been described in detail elsewhere.15Cases were assigned an arbitrary and anonymous unique identifier and the same basic demographic variables as those collated for GP cases were extracted. Data analysisAge and ethnicity-specific skin infection rates from participating GP registers were directly standardised to the regional population to give an estimate of the total number and rate of skin infection cases seen in children in primary care in the Tairawhiti region. Confidence intervals (CIs) were constructed using the methods of Clayton and Hills.16 Denominators in rate calculations were based on usually resident population counts from the 2006 Census. Annual infection rates were calculated from extrapolations of observed data. Seasonal adjustment was not made as recent work has shown there is very little seasonality in hospitalisation rates for skin infections in the Tairawhiti region compared to NZ (see companion articles in this issue of the New Zealand Medical Journal) and it is unknown whether rates of skin infections in primary care exhibit seasonal trends. The ethnicity and gender distribution of children in general practice and in the hospital setting were compared using the Fishers exact test. Age distributions were compared using the Mann Whitney U test. A two-tailed p-value of less than 0.05 was considered statistically significant. Regional Ethics Committee approval was obtained for this study. Results Incidence and characteristics of skin infection cases in primary careOver the 10-week data collection period, 110 incident cases of skin infections in 107 children were recorded by the nine participating GPs. Table 1 summarises the observed number and rate of cases in each age and ethnicity group. Based on age and ethnicity standardisation of observed rates, there were an estimated 378.6 (95%CI: 312.4-458.9) cases of skin infections seen in primary care, equivalent to a rate of 20.5 cases (95%CI: 16.9 to 24.9) per 1000 0-14-year-old children in the Tairawhiti region during the 10-week study period (see Table 1). Extrapolating these data longitudinally, without taking seasonal adjustment into account, there were an estimated 1968.7 (95%CI: 1624.5-2386.3) cases of skin infections in children in the Tairawhiti region primary care setting during 2008. This frequency is equivalent to an annual incidence rate of 106.7 (95%CI: 85.2-127.2) per 1000 children in the region, or 10.7% of the population if there were no repeat infections in the same individuals. In M ori children, there was a trend towards reducing case incidence with increasing age. This trend was less apparent in non-M ori children. Annual infection rates ranged from 29.0 per 1000 for non-M ori children aged 10-14 years, up to 245.5 per 1000 for M ori children aged 0-4 years. Table 1. Skin infection incidence observed in the study population, and estimated for the Tairawhiti region, 0-14 year old children, May-July 2008 Ethnicity/age group Observed case rate per 1000 2020 (no. of cases/no. at risk) Tairawhiti region population 2021 Estimated no. of primary care cases in Tairawhiti region 00a7 Estimated annual rate of primary care cases in Tairawhiti region# M ori 0-4 years 5-9 years 10-14 years 47.2 (34/720) 42.6 (33/774) 24.0 (18/751) 2163 2241 2403 102.1 95.4 57.6 245.5 221.4 124.6 Non-M ori 0-4 years 5-9 years 10-14 years 11.9 (8/671) 14.8 (12/813) 5.6 (5/898) 3651 3852 4146 43.5 56.9 23.1 62.0 76.8 29.0 Total 20.5 (95%CI: 16.9-24.9) 18,456 378.6 (95%CI: 312.4-458.9) 106.7 (95%CI: 85.2-127.2) 95% CI: 95% confidence interval; No.: number. 2020 Ethnicity and age-specific rates of skin infections observed in participating primary care practices during 10-week study period. 2021 Based on usually resident population data in 2006 Census. 00a7 Estimated number of primary care cases of skin infection in children in the Tairawhiti region during the 10-week study period, based on multiplying the age and ethnicity specific rates observed in participating GP practices by the Tairawhiti region population for that age/ethnicity group. # Estimated annual rate per 1000 of primary care cases of skin infection in the Tairawhiti region, based on annualising the 10-week rate (without seasonal adjustment). Comparing skin infection cases seen in primary care and hospital settingsDuring the same 10-week data collection period, 27 cases of serious skin infection in 27 children were admitted to Gisborne Hospital. Based on the estimated 378.6 primary care skin infection cases in the region over this period, there were 14 primary care cases for every one hospitalised serious skin infection. Table 2 and Figure 1 summarise and compare the basic demographic characteristics of primary care and hospital cases seen over the same period in 2008. Most primary care cases were coded only to the minimum code level of M0.00, so information on subtypes of skin infection and free-text diagnosis description was not available. There was a significant difference in the age distribution of skin infection cases between the two settings (p=0.0041). Preschool-aged children accounted for two-thirds (67%) of hospitalised cases of serious skin infection but only 38% of infections in primary care. While just 15% of hospitalised cases were in children aged 5-9 years, this group made up the largest proportion of cases in primary care (41%). The 10-14 year old age group accounted for the smallest proportion of cases overall. Slightly more boys were admitted to hospital with a serious skin infection than girls, 56% and 44% respectively, but this difference did not reach statistical significance. There was no gender predominance in primary care cases with equal numbers of male and female children suffering skin infections. The difference between settings was not significant (p=0.67). Just over three-quarters (77%) of skin infection cases in the primary care setting were in M ori children. Hospitalised cases of serious skin infections exhibited a similar ethnic distribution, with 78% occurring in M ori children (p 1.00). Table 2. Comparison of the demographic characteristics of children with skin infections seen in primary care and hospital settings in the Tairawhiti region, May-July 2008 Variable Primary care cases Hospital cases Difference No. PP (95% CI) No. PH (95% CI) PP - PH p Age (yrs) 0-4 5-9 10-14 42 45 23 0.38(0.30-0.48) 0.41(0.32-0.50) 0.21(0.14-0.29) 18 4 5 0.67(0.48-0.81) 0.15(0.05-0.33) 0.18(0.08-0.37) - 0.29 +0.26 +0.03 0.004 Gender Male Female 55 55 0.50(0.41-0.59) 0.50(0.41-0.59) 15 12 0.56(0.37-0.72) 0.44(0.28-0.63) - 0.06 +0.06 0.67 Ethnicity M ori Non-M ori