Pilot Report on Surveillance of Paediatric Respiratory Syncytial Virus

Transcription

1 Pilot Report on Surveillance of Paediatric Respiratory Syncytial Virus BACKGROUND Health Department Letter (2001)57 requires that trusts undertake surveillance of HAI. The national HAI Surveillance Steering Group developed a working group to oversee development of HAI surveillance in paediatrics. Surveillance of RSV was the first programme of surveillance focussed upon in recognition of the fact that it is the most common respiratory pathogen in infants and young children affecting nearly all children by the age of two years 1. The very young and those with predisposing conditions are most at risk from complications and nosocomial outbreaks in paediatric units can be a major problem 2. Surveillance of nosocomial viral infections allows the rapid detection of outbreaks of HAI and the prompt initiation of prevention procedures. Respiratory syncytial virus (RSV) infection is a common cause of respiratory infection in young children resulting usually in bronchiolitis and pneumonia and is a common nosocomial pathogen during the seasonal outbreak period. The incidence of nosocomial infection has been estimated at 7.2/1000 in-patient days and in one study it was found that 40% of children in hospital for more than one week acquired the infection. RSV is transmitted through contact with infected respiratory secretions. Transmission by contaminated fomites has been demonstrated. INTRODUCTION Respiratory Syncytial Virus( RSV) is a respiratory infection which can occur throughout life. During the first few months of childhood approximately 20% of all infants infected with the virus experience lower respiratory tract complications and in this period up to 3% are hospitalised with bronchiolitis or pneumonia 3. Children with underlying health conditions in developed countries have an increased risk of developing RSV particularly those infants who are born premature are immunosupressed or have chest or lung disease 4. This virus is spread by droplets that are expelled from the respiratory tract of the infected individual and then transmitted by hands that have been in contact with the responsible organism. Children that are admitted to hospital infected with the virus are a potential source of infection to fellow patients, staff and visitors 5. A large percentage of nosocomial viral pneumonias are caused by respiratory syncytyial virus which frequently affect children particularly throughout the winter period. These predictable annual outbreaks of RSV are a major cause of respiratory tract infection in all age groups. The majority of infected, otherwise healthy infants can be managed in the community, however, hospitalisation is on the increase for infants infected 3.

2 OBJECTIVES OF PROJECT To monitor trends in the incidence of RSV To examine the feasibility of the methods proposed in this pilot study for national RSV surveillance in Scotland DEFINITIONS The definition of a definite nosocomial acquired case of RSV was defined as a patient with respiratory symptoms (poor feeding, apnoea in infants) or who is asymptomatic following an inpatient stay of 7 days or more with a subsequent RSVpositive nasopharyngeal aspirate. A possible case was defined as a patient with respiratory symptoms or one who is asymptomatic within 3 to 6 days of admission who is subsequently found to be RSV-positive. METHODS Two acute paediatric hospitals agreed to take part in a pilot of the methodology during the RSV season i.e. 1 st November 2002 to 31 st March The study design was prospective cohort surveillance and data were collected on each nosocomial RSV case along with details of throughput data and details of the level of community acquired RSV admissions to each clinical area in the study. Patients were identified through laboratory reporting or near patient testing on a daily basis and the infection control team informed by nursing staff. (If a patient was discharged on pass for more than 24 hours and subsequently developed an RSV infection, this was recorded as a possible nosocomial case). Once a positive RSV had been identified a data collection form was completed by the Infection Control Nurse. The two sites chose differing methods of managing their data with one completing a TELEform form for each nosocomial infection while the other extracted the data from their ongoing surveillance programme. ANALYSES The study protocol indicated that for each clinical area/ward within the study the following statistics were to be produced: Total Occupied Beds Total RSV Beds Community Acquired RSV Bed Days Nosocomial RSV Bed Days Number of Community Acquired RSV Admissions Number of Nosocomial RSV Cases Average Bed Days per Nosocomial Case At Risk Bed Days Potential Exposure Risk Ratio Incidence Density per 1000 At-Risk Days

3 Reporting of incidence density of seasonal nosocomial RSV measures the rate for susceptible populations within and between institutions during the risk period. Use of statistics like the potential exposure risk ratio allow us to quality the burden of disease with units and help to explain differences in the incidence of nosocomial infection rates. RESULTS Total Occupied Beds More than 21,000 bed days were included in the study. The number of bed days varied substantially between clinical areas depending on the specialty of the included wards (range: 435 to 2754). Total RSV bed days The total RSV bed days varied greatly between wards (range: 0 to 1153 days) and was used to estimate the burden of disease within each ward and to evaluate the risk of cross-infection. Community acquired RSV bed days This measure indicates the level of community acquired disease within each ward and shows large levels of infection in both hospitals, with over 10% of bed days in the areas under study occupied by RSV patients (2172 bed days of 21,269) Nosocomial RSV bed days This shows the level of hospital acquired RSV present in the wards over the study period and varies widely between clinical areas with several wards having no nosocomial bed days. Number of nosocomial RSV cases The number of patients acquiring a RSV infection as an inpatient and meeting the case definition. The majority of wards did not have any nosocomial cases. Although the number of community acquired RSV patients admitted to the two hospitals was over 400, the number of patients developing a hospital acquired RSV infection was only 6 (five definite and one possible infection). Average bed days per nosocomial case

4 The average length of stay per nosocomial case (calculated by total nosocomial bed days/number of nosocomial cases). The average length of stay for community acquired cases was 7 days compared to 48 days for hospital acquired cases. At risk bed days The number of patient days in which a patient who is negative for RSV is in the same ward as a positive patient. This measure provides an indication of the potential for cross-infection to occur. A total of 15,943 at-risk bed days were accrued over the study period. Potential exposure risk ratio The potential exposure risk ratio (PER) is calculated by dividing the number of community-acquired RSV bed-days by the number of patient days of exposure to active community-acquired cases. In our study the overall PER was low (1:0.14) with 86% fewer community acquired RSV bed days that at-risk bed days. Incidence density per 1000 at-risk days Incidence density monitoring of cross-infection can provide reliable feedback on the outcome of control measures. The incidence of definite or possible nosocomial RSV cases covered the range from 0 to 11.4 cases per 1000 patient days and overall was per 1000 patient days, this compares favourably with published results 6. The summary statistics for each ward in hospital 1 are shown in table 1 and for hospital 2 are shown in table 2. Table 3 shows the results for all areas together. Table 1 : Summary statistics for RSV transmission and risk in Hospital 1 Ward Total Total Occupied Beds Total RSV Beds Community Acquired RSV Bed Days Nosocomial RSV Bed Days Number of Community Acquired RSV Admissions Number of Nosocomial RSV Cases Average Bed Days per Nosocomial Case 16 N/A 32 N/A N/A At Risk Bed Days Potential Exposure Risk Ratio Incidence Density per 1000 At-Risk Days

5 Table 2 : Summary statistics for RSV transmission and risk in Hospital 2 Ward Total Total Occupied Beds Total RSV Beds Community Acquired RSV Bed Days Nosocomial RSV Bed Days Number of Community Acquired RSV Admissions Number of Nosocomial RSV Cases Average Bed Days per Nosocomial Case At Risk Bed Days Potential Exposure Risk Ratio Incidence Density per 1000 At-Risk Days Table 3: Overall Summary Statistics for RSV transmission OVERALL Total Occupied Beds Total RSV Beds 2458 Community Acquired RSV Bed Days 2172 Nosocomial RSV Bed Days 286 Number of Community Acquired RSV Admissions 405 Number of Nosocomial RSV Cases 6 Average Bed Days per Nosocomial Case At Risk Bed Days Potential Exposure Risk Ratio Incidence Density per 1000 At-Risk Days Discussion The majority of RSV presented in paediatric acute care and were community-acquired with very few hospital-acquired cases. Although the proportion of beds occupied by community acquired RSV appear high within the wards studied, the cross infection rates reported were low. This perhaps reflects the low level of RSV during the study period which consequently reduced the burden on resources allowing good infection control practices to be maintained. Other possible contributing factors: Staff infection control education programmes re risk factors, prevention, treatment and outcomes Isolation precautions and facilities Community treatment of otherwise healthy patients Adequate staffing levels / low agency use Reduced length of patient stay Nosocomial RSV in discharged pts /underestimated?

6 No explanation / all of above and seasonal low?? Conclusions/Recommendations The REP in our study was low (0.14:1) with 86% fewer community-acquired RSV bed days that at-risk bed days. The PER may be a useful tool for making comparisons between years and it is proposed that the surveillance be carried out during the next RSV season. The majority of the data collection burden for this study fell upon the infection control nurses of the two hospitals and an important aspect of the study was to ascertain the level of this burden. Although the small number of nosocomial cases may have reduced the workload associated with this, it was generally felt that this was a worthwhile exercise and should be continued in subsequent years. References 1. Wyde PR, Respiratory syncytial virus (RSV) disease and prospects for its control. Antiviral Research 1998;39: Collins CL, Pollard AJ, Respiratory syncytial virus infections in children and adults. Science and Clinical Practice 2002;45: Meissner CH, Selected populations at increased risk from respiratory syncytial virus infection. Pediatric Infectious Disease Journal 2003;22: S40-S45 4. Howard TS et al, Respiratory syncytial virus pneumonia in the hospital setting: Length of stay, charges and mortality. The Journal of Pediatrics 2000;137: Wilson J, Preventing Infection of the Respiratory Tract p In: Infection Control in Clinical Practice. Ballière Tindall (London) 6. McLaws ML et al, Rate of seasonal spread of respiratory syncytial virus in a paediatric hospital. Infection Control and Hospital Epidemiology 1997;18: Appendix I WORKING GROUP MEMBERSHIP Dr Ahilya Noone, Consultant Epidemiologist, SCIEH Dr Rosie Hague, Consultant Infectious Diseases, RHSC, Yorkhill Dr Alison Balfour, Consultant Microbiologist, RHSC, Yorkhill Dr Ian Gould, Consultant Microbiologist, Aberdeen Childrens Hospital

7 Dr Pota Kalima, Consultant Microbiologist, Western General Hospital, Edinburgh Dr Peter Mackie, Clinical Scientist, RHSC, Yorkhill Mrs Pamela Joannidis, Infection Control, RHSC, Yorkhill Dr Nick Hallam, Consultant Virologist, Edinburgh Royal Infirmary, Little France, Edinburgh Ms Audrey Mackenzie, Infection Control, Royal Hospital for Sick Children, Edinburgh Mrs Angela Johnson, Infection Control, RHSC, Yorkhill Mr Robert Hill, Epidemiologist, SCIEH