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Nosocomial H1N1 infection during 2010–2011 pandemic: a retrospective cohort study from a tertiary referral hospital
Journal of Hospital Infection 81 (2012) 202e205 Available online at www.sciencedirect.com
Journal of Hospital Infection journal homepage: www.elsevierhealth.com/journals/jhin
Short report
Nosocomial H1N1 infection during 2010e2011 pandemic: a retrospective cohort study from a tertiary referral hospitalq T. Veenith a, F. Sanfilippo b, c, A. Ercole a, E. Carter b, N. Goldman a, P.G. Bradley a, K. Gunning a, R.M. Burnstein b, * a
John Farman Intensive Care Unit, Cambridge University Hospitals NHS Trust, Cambridge, UK Neuro Critical Care Unit, Cambridge University Hospitals NHS Trust, Cambridge, UK c Department of Experimental and Clinical Pharmacology, University of Catania, School of Medicine, Catania, Italy b
A R T I C L E
I N F O
Article history: Received 11 January 2012 Accepted 9 April 2012 Available online 1 June 2012 Keywords: Critical care unit H1N1 Hospital-acquired H1N1 influenza Vaccine
S U M M A R Y
This study aimed to estimate the incidence of hospital transmission of influenza A subtype H1N1 [A(H1N1)], to identify high-risk areas for such transmission and to evaluate common characteristics of affected patients. In this single-centre retrospective cohort study, 10 patients met the criteria for hospital-acquired A(H1N1) infection over a three-month period. All affected patients required an escalation of their care and the mortality rate was 20%. Clinicians should be aware of the risk of nosocomial A(H1N1) infection that exists despite routine infection control measures and should consider additional control measures including vaccination of hospital inpatients and healthcare staff. Ó 2012 Published by Elsevier Ltd on behalf of the Healthcare Infection Society.
Introduction The A(H1N1) pandemic influenza virus is a product of the triple reassortment of human, avian and swine H1N1 viruses and can cause severe respiratory failure.1 Nosocomial transmission of influenza is a recognized problem for vulnerable patients including paediatric, immunosuppressed, haemoncological patients and the elderly. A(H1N1) influenza is spread by bio-aerosols (<5 mm diameter) and droplets (20 mm diameter), which may be generated in the hospital environment by cough, chest physiotherapy and ventilation.2 These q Presented and elected as best free research paper in State of Art Meeting, London, 2011. * Corresponding author. Address: Neuro Critical Care Unit, Cambridge University Hospitals NHS Trust, Hills Road, Cambridge CB2 0QQ, UK. E-mail address: [email protected] (R.M. Burnstein).
aerosols can travel >2 m and are detectable for up to 24 h after their release. Influenza virus can survive on non-porous surfaces for 24e48 h, on porous surfaces for up to 12 h and on the hands of care providers for up to 5 min.2 This study aimed to estimate the incidence of hospital transmission of A(H1N1), to identify the high-risk areas for transmission, and to assess any common characteristics of affected patients.
Methods The National Research Ethics Committee reviewed this retrospective cohort study and a waiver of consent was issued (Ref.: 04/02). The study included all inpatients in a tertiary referral hospital (Cambridge University Hospitals NHS Trust) between November 2010 and January 2011 who had a positive A(H1N1) polymerase chain reaction (PCR). Data obtained from the medical notes and general practitioners included patient demography, medical history, A(H1N1) influenza vaccination
0195-6701/$ e see front matter Ó 2012 Published by Elsevier Ltd on behalf of the Healthcare Infection Society. doi:10.1016/j.jhin.2012.04.010
Table I Characteristics of patients with hospital-acquired A(H1N1) influenza Patient Age LOS in ITU/HDU no. (years) hospital admission (days) 67
32
2
79
12
3
27
53
4
68
90
5
44
71
6
21
77
7
44
75
8
29
45
9
42
84
10
57
62
HDU
Yes: radiotherapy
Medical history
Plasmacytoma undergoing radiotherapy HDU Yes: steroids Admitted with bilateral pulmonary embolism, on steroids for polymyalgia rheumatic ITU/HDU No Admitted with Budd Chiari, past history of nephrotic syndrome ITU No Admitted with acute or chronic liver failure ITU No Multiple sclerosis admitted with urosepsis, treated then developed sudden respiratory failure requiring CPAP HDU Yes: Post-stem-cell transplant for immunosuppressants anaplastic large cell lymphoma ITU Yes: steroids Acute renal failure secondary to vasculitis (ANCA positive) ITU Yes: post transplant Admitted for orthotopic liver transplant (sclerosing cholangitis), acute rejection followed by redo surgery ITU No Admitted with epidural abscess and C6e7 discitis with cord compression, operated ITU No Post-cardiac surgery following an acute MI, coronary bypass graft and mitral valve replacement
Sex
LOS before PCR/symptoms
Outcome
Vaccination Antiviral Escalation status therapy of treatment
M
5 days
Died
No
Yes
Yes
F
6 days
Discharged
Yes
Yes
Yes
M
6 days
Discharged
No
Yes
Yes
M
9 days
Died
No
Yes
No
F
10 days
Discharged
Yes
Yes
Yes
M
12 days
Discharged
No
Yes
Yes
M
12 days
Discharged
No
Yes
No
M
25 days
Discharged
No
Yes
No
F
28 days
Rehabilitation
No
Yes
No
M
49 days
Discharged
No
Yes
No
T. Veenith et al. / Journal of Hospital Infection 81 (2012) 202e205
1
Immunodeficiency
HDU, high dependency unit; ITU, intensive therapy unit; LOS, length of stay; PCR, polymerase chain reaction; CPAP, continuous positive airways pressure; ANCA, anti-neutrophil cytoplasmic antibodies; MI, myocardial infarction.
203
204
T. Veenith et al. / Journal of Hospital Infection 81 (2012) 202e205
history, relevant timelines, treatments given during this admission and outcome. Hospital-acquired A(H1N1) influenza [HA-A(H1N1)] was defined as a positive PCR with symptoms after admission with an unrelated illness, after the incubation period suggested by the Centers for Disease Control and Prevention (1e4 days) and without any ‘flu-like’ symptoms on admission. To exclude false positives for HA-A(H1N1), the longest incubation period (five days) was used as the minimum duration between hospital admission and PCR positivity. Patients included were followed up for the next three months to ascertain the outcome from their hospital admission. Escalation of treatment was defined as a transfer from a non-critical care area to a critical care area. Patients were considered immunosuppressed if they were taking immunosuppressant or anti-rejection drugs, undergoing plasmapheresis, radiotherapy or chemotherapy.
the infection. The patients who acquired A(H1N1) infection outside critical care areas also required respiratory support escalation, either in a critical care area or respiratory ward. Only two (20%) of the patients who contracted HA-A(H1N1) had received the A(H1N1) vaccination. The majority of the other patients would have been eligible for influenza vaccination due to age or concurrent medical conditions. Unfortunately the information was not available to assess whether they had been offered vaccination prior to hospital admission. Following HA-A(H1N1) diagnosis, all the patients received a course of the neuraminidase inhibitor, oseltamivir. Two of the patients died while in hospital and both patients had serious underlying medical conditions (Table I). The other eight patients were all discharged from hospital. The length of hospital stay varied from 12 to 84 days (median: 67).
Discussion Results Between November 2010 and January 2011, 86 patients were identified with (reverse transcriptase PCR) influenza A(H1N1) infection. Of these 86 patients, 10 (12%) patients met the criteria for HA-A(H1N1) (Figure 1). The ages of the patients with HA-A(H1N1) ranged from 21 to 79 years (median: 44). Eight (80%) patients had serious underlying illnesses and five (50%) were receiving immunosuppressive therapy. Seven (70%) of the patients were admitted for medical treatment of acute illnesses or ongoing management of their underlying illnesses and the other three patients were admitted for surgical procedures. The length of hospital admission prior to symptoms and positive PCR varied from 5 to 49 days (median: 11). Seven (70%) patients developed HA-A(H1N1) infection more than 7 days after admission. Five (50%) patients acquired A(H1N1) infection while in a critical care unit and all needed an escalation or prolongation of intensive ventilatory support after contracting
Hospitals are crowded places in which a reservoir of infection and a vulnerable cohort of patients coexist. This study suggests that significant transmission of A(H1N1) infection occurs in a tertiary hospital setting and that affected patients have a high mortality (20%). Patient groups that appear vulnerable include those on critical care units, the immunocompromised and those with a protracted hospital stay. Even with strict infection control measures, hospital transmission of A(H1N1) will never be totally preventable and it is therefore essential to consider alternative methods to reduce nosocomial A(H1N1) infection. An in-hospital vaccination programme for all patients admitted during an influenza pandemic warrants further evaluation. It is not only potentially in the patients’ best interests, but also could be resource-sparing by decreasing critical care requirements and preventing prolonged hospital admissions. A(H1N1) antibody production takes two weeks which is clearly a limitation.3 However, in our study 70% of patients developed
Hospital patients with confirmed positive PCR for H1N1 N = 86
Patients with hospital-acquired A(H1N1) infection N = 10
Vaccinated patients N=2
Non-vaccinated patients N=8
Immunosuppressed patients N=4
Patients admitted to hospital with A(H1N1) infection N = 76
Non-immunosuppressed patients N=4
Immunosuppressed patient N=1
Figure 1. Vaccination status of patients with influenza A subtype H1N1.
T. Veenith et al. / Journal of Hospital Infection 81 (2012) 202e205 A(H1N1) infection 7 days after hospital admission, suggesting that in-hospital vaccination could be effective for some patients. Vaccination might also help to reduce the risk of vulnerable patients being readmitted to hospital with community-acquired A(H1N1). The safety of the vaccination programme is well established, with more than 42.5 million doses of H1N1 vaccines administered across Europe (data from Medicines and Healthcare Products Regulatory Agency up to March 2010). Concerns exist regarding vaccination in the immunocompromised host but studies of children undergoing immunomodulatory therapy demonstrate that the vaccine is well tolerated.4 In addition, solid organ transplant patients appear to tolerate vaccination well despite initial concerns that the activation of non-specific cellular immunity might trigger organ rejection.5 Smaller vaccination responses may occur, but it has been demonstrated that the immunocompromised population can still achieve sufficient antibody titres and a second influenza vaccine dose may be given to ensure an adequate response.6 These safety and efficacy data suggest that implementing a vaccination programme in all high-risk patients on admission to hospital should be considered. Serological testing is unfortunately inaccurate as there is an absence of cross-reactivity between influenza strains and interpretation of results is challenging particularly in the immunocompromised population.7,8 A serological testing programme would therefore not be of use when deciding which patients should receive a second vaccine dose. Healthcare workers are a potential source of A(H1N1) nosocomial infection. Research indicates that healthcare workers often continue working during influenza infections, especially if symptoms are mild, and they risk transmitting the virus to their patients.9 Data from the Department of Health indicate that only 30% of frontline healthcare workers at CUH NHS Trust received the seasonal influenza vaccine in winter 2010/11. Mandatory vaccination programmes have been the most effective means of increasing vaccination rates in healthcare workers but the UK has chosen so far not to adopt this approach.10 Limitations of this study include being performed in a single centre with a small population sample and that the impact on the duration of hospital admission could not be assessed. Restricting the incubation period to five days or more may also have missed some cases of HA-A(H1N1). This study should prompt more research into prevention of transmission in vulnerable patients. Visiting restrictions and staff vaccination may reduce in-hospital transmission. Further data are needed to assess the effectiveness of in-hospital vaccination against A(H1N1) and the use of additional doses of vaccine in vulnerable patients. In conclusion, HA-A(H1N1) infection is a common entity accounting for more than 10% of all inpatient cases of A(H1N1)
205
influenza. Care should be taken to identify the ‘at-risk’ population and further studies are required to define the potential role and effectiveness of vaccination in preventing such infection.
Acknowledgements We thank Mrs Bushen and Dr E.F. Wallin for help with data acquisition. Conflict of interest statement None declared. Funding sources Dr T. Veenith is supported by National Institute of Academic Anaesthesia on a Clinical Research Training Fellowship, and Raymond and Beverly Sackler studentship.
References 1. Miller RR, Markewitz BA, Rolfs RT, et al. Clinical findings and demographic factors associated with ICU admission in Utah due to novel 2009 influenza A(H1N1) infection. Chest 2010;137:752e758. 2. Simonds AK, Hanak A, Chatwin M, et al. Evaluation of droplet dispersion during non-invasive ventilation, oxygen therapy, nebuliser treatment and chest physiotherapy in clinical practice: implications for management of pandemic influenza and other airborne infections. Health Technol Assessmnt 2010;14:131e172. 3. Girard M, Tam J, Assossou O, Kieny M. The 2009 A (H1N1) influenza virus pandemic: a review. Vaccine 2010;28:4895e4902. 4. Esposito S, Cecinati V, Russo FG, Principi N. Influenza vaccination in children with cancer receiving chemotherapy. Hum Vaccin 2009;5:430e432. 5. Torii Y, Kimura H, Ochi N, et al. Immunogenicity of inactivated 2009 H1N1 influenza vaccine in pediatric liver transplant recipients. Vaccine 2011;29:4187e4189. 6. Pollyea DA, Brown JMY, Horning SJ. Utility of influenza vaccination for oncology patients. J Clin Oncol 2010;28:2481e2490. 7. Kunisaki KM, Janoff EN. Influenza in immunosuppressed populations: a review of infection frequency, morbidity, mortality, and vaccine responses. Lancet Infect Dis 2009;9:493e504. 8. McVernon J, Laurie K, Barr I, Kelso A, Skeljo M, Nolan T. Absence of cross-reactive antibodies to influenza A (H1N1) 2009 before and after vaccination with 2009 Southern Hemisphere seasonal trivalent influenza vaccine in children aged 6 monthse9 years: a prospective study. Influenza Other Respir Viruses 2011;5:7e11. 9. Elder AG, O’Donnell B, McCruden EA, Symington IS, Carman WF. Incidence and recall of influenza in a cohort of Glasgow healthcare workers during the 1993e4 epidemic: results of serum testing and questionnaire. BMJ 1996;313:1241e1242. 10. Babcock HM, Gemeinhart N, Jones M, Dunagan WC, Woeltje KF. Mandatory influenza vaccination of health care workers: translating policy to practice. Clin Infect Dis 2010;50:459e464.
Journal of Hospital Infection journal homepage: www.elsevierhealth.com/journals/jhin
Short report
Nosocomial H1N1 infection during 2010e2011 pandemic: a retrospective cohort study from a tertiary referral hospitalq T. Veenith a, F. Sanfilippo b, c, A. Ercole a, E. Carter b, N. Goldman a, P.G. Bradley a, K. Gunning a, R.M. Burnstein b, * a
John Farman Intensive Care Unit, Cambridge University Hospitals NHS Trust, Cambridge, UK Neuro Critical Care Unit, Cambridge University Hospitals NHS Trust, Cambridge, UK c Department of Experimental and Clinical Pharmacology, University of Catania, School of Medicine, Catania, Italy b
A R T I C L E
I N F O
Article history: Received 11 January 2012 Accepted 9 April 2012 Available online 1 June 2012 Keywords: Critical care unit H1N1 Hospital-acquired H1N1 influenza Vaccine
S U M M A R Y
This study aimed to estimate the incidence of hospital transmission of influenza A subtype H1N1 [A(H1N1)], to identify high-risk areas for such transmission and to evaluate common characteristics of affected patients. In this single-centre retrospective cohort study, 10 patients met the criteria for hospital-acquired A(H1N1) infection over a three-month period. All affected patients required an escalation of their care and the mortality rate was 20%. Clinicians should be aware of the risk of nosocomial A(H1N1) infection that exists despite routine infection control measures and should consider additional control measures including vaccination of hospital inpatients and healthcare staff. Ó 2012 Published by Elsevier Ltd on behalf of the Healthcare Infection Society.
Introduction The A(H1N1) pandemic influenza virus is a product of the triple reassortment of human, avian and swine H1N1 viruses and can cause severe respiratory failure.1 Nosocomial transmission of influenza is a recognized problem for vulnerable patients including paediatric, immunosuppressed, haemoncological patients and the elderly. A(H1N1) influenza is spread by bio-aerosols (<5 mm diameter) and droplets (20 mm diameter), which may be generated in the hospital environment by cough, chest physiotherapy and ventilation.2 These q Presented and elected as best free research paper in State of Art Meeting, London, 2011. * Corresponding author. Address: Neuro Critical Care Unit, Cambridge University Hospitals NHS Trust, Hills Road, Cambridge CB2 0QQ, UK. E-mail address: [email protected] (R.M. Burnstein).
aerosols can travel >2 m and are detectable for up to 24 h after their release. Influenza virus can survive on non-porous surfaces for 24e48 h, on porous surfaces for up to 12 h and on the hands of care providers for up to 5 min.2 This study aimed to estimate the incidence of hospital transmission of A(H1N1), to identify the high-risk areas for transmission, and to assess any common characteristics of affected patients.
Methods The National Research Ethics Committee reviewed this retrospective cohort study and a waiver of consent was issued (Ref.: 04/02). The study included all inpatients in a tertiary referral hospital (Cambridge University Hospitals NHS Trust) between November 2010 and January 2011 who had a positive A(H1N1) polymerase chain reaction (PCR). Data obtained from the medical notes and general practitioners included patient demography, medical history, A(H1N1) influenza vaccination
0195-6701/$ e see front matter Ó 2012 Published by Elsevier Ltd on behalf of the Healthcare Infection Society. doi:10.1016/j.jhin.2012.04.010
Table I Characteristics of patients with hospital-acquired A(H1N1) influenza Patient Age LOS in ITU/HDU no. (years) hospital admission (days) 67
32
2
79
12
3
27
53
4
68
90
5
44
71
6
21
77
7
44
75
8
29
45
9
42
84
10
57
62
HDU
Yes: radiotherapy
Medical history
Plasmacytoma undergoing radiotherapy HDU Yes: steroids Admitted with bilateral pulmonary embolism, on steroids for polymyalgia rheumatic ITU/HDU No Admitted with Budd Chiari, past history of nephrotic syndrome ITU No Admitted with acute or chronic liver failure ITU No Multiple sclerosis admitted with urosepsis, treated then developed sudden respiratory failure requiring CPAP HDU Yes: Post-stem-cell transplant for immunosuppressants anaplastic large cell lymphoma ITU Yes: steroids Acute renal failure secondary to vasculitis (ANCA positive) ITU Yes: post transplant Admitted for orthotopic liver transplant (sclerosing cholangitis), acute rejection followed by redo surgery ITU No Admitted with epidural abscess and C6e7 discitis with cord compression, operated ITU No Post-cardiac surgery following an acute MI, coronary bypass graft and mitral valve replacement
Sex
LOS before PCR/symptoms
Outcome
Vaccination Antiviral Escalation status therapy of treatment
M
5 days
Died
No
Yes
Yes
F
6 days
Discharged
Yes
Yes
Yes
M
6 days
Discharged
No
Yes
Yes
M
9 days
Died
No
Yes
No
F
10 days
Discharged
Yes
Yes
Yes
M
12 days
Discharged
No
Yes
Yes
M
12 days
Discharged
No
Yes
No
M
25 days
Discharged
No
Yes
No
F
28 days
Rehabilitation
No
Yes
No
M
49 days
Discharged
No
Yes
No
T. Veenith et al. / Journal of Hospital Infection 81 (2012) 202e205
1
Immunodeficiency
HDU, high dependency unit; ITU, intensive therapy unit; LOS, length of stay; PCR, polymerase chain reaction; CPAP, continuous positive airways pressure; ANCA, anti-neutrophil cytoplasmic antibodies; MI, myocardial infarction.
203
204
T. Veenith et al. / Journal of Hospital Infection 81 (2012) 202e205
history, relevant timelines, treatments given during this admission and outcome. Hospital-acquired A(H1N1) influenza [HA-A(H1N1)] was defined as a positive PCR with symptoms after admission with an unrelated illness, after the incubation period suggested by the Centers for Disease Control and Prevention (1e4 days) and without any ‘flu-like’ symptoms on admission. To exclude false positives for HA-A(H1N1), the longest incubation period (five days) was used as the minimum duration between hospital admission and PCR positivity. Patients included were followed up for the next three months to ascertain the outcome from their hospital admission. Escalation of treatment was defined as a transfer from a non-critical care area to a critical care area. Patients were considered immunosuppressed if they were taking immunosuppressant or anti-rejection drugs, undergoing plasmapheresis, radiotherapy or chemotherapy.
the infection. The patients who acquired A(H1N1) infection outside critical care areas also required respiratory support escalation, either in a critical care area or respiratory ward. Only two (20%) of the patients who contracted HA-A(H1N1) had received the A(H1N1) vaccination. The majority of the other patients would have been eligible for influenza vaccination due to age or concurrent medical conditions. Unfortunately the information was not available to assess whether they had been offered vaccination prior to hospital admission. Following HA-A(H1N1) diagnosis, all the patients received a course of the neuraminidase inhibitor, oseltamivir. Two of the patients died while in hospital and both patients had serious underlying medical conditions (Table I). The other eight patients were all discharged from hospital. The length of hospital stay varied from 12 to 84 days (median: 67).
Discussion Results Between November 2010 and January 2011, 86 patients were identified with (reverse transcriptase PCR) influenza A(H1N1) infection. Of these 86 patients, 10 (12%) patients met the criteria for HA-A(H1N1) (Figure 1). The ages of the patients with HA-A(H1N1) ranged from 21 to 79 years (median: 44). Eight (80%) patients had serious underlying illnesses and five (50%) were receiving immunosuppressive therapy. Seven (70%) of the patients were admitted for medical treatment of acute illnesses or ongoing management of their underlying illnesses and the other three patients were admitted for surgical procedures. The length of hospital admission prior to symptoms and positive PCR varied from 5 to 49 days (median: 11). Seven (70%) patients developed HA-A(H1N1) infection more than 7 days after admission. Five (50%) patients acquired A(H1N1) infection while in a critical care unit and all needed an escalation or prolongation of intensive ventilatory support after contracting
Hospitals are crowded places in which a reservoir of infection and a vulnerable cohort of patients coexist. This study suggests that significant transmission of A(H1N1) infection occurs in a tertiary hospital setting and that affected patients have a high mortality (20%). Patient groups that appear vulnerable include those on critical care units, the immunocompromised and those with a protracted hospital stay. Even with strict infection control measures, hospital transmission of A(H1N1) will never be totally preventable and it is therefore essential to consider alternative methods to reduce nosocomial A(H1N1) infection. An in-hospital vaccination programme for all patients admitted during an influenza pandemic warrants further evaluation. It is not only potentially in the patients’ best interests, but also could be resource-sparing by decreasing critical care requirements and preventing prolonged hospital admissions. A(H1N1) antibody production takes two weeks which is clearly a limitation.3 However, in our study 70% of patients developed
Hospital patients with confirmed positive PCR for H1N1 N = 86
Patients with hospital-acquired A(H1N1) infection N = 10
Vaccinated patients N=2
Non-vaccinated patients N=8
Immunosuppressed patients N=4
Patients admitted to hospital with A(H1N1) infection N = 76
Non-immunosuppressed patients N=4
Immunosuppressed patient N=1
Figure 1. Vaccination status of patients with influenza A subtype H1N1.
T. Veenith et al. / Journal of Hospital Infection 81 (2012) 202e205 A(H1N1) infection 7 days after hospital admission, suggesting that in-hospital vaccination could be effective for some patients. Vaccination might also help to reduce the risk of vulnerable patients being readmitted to hospital with community-acquired A(H1N1). The safety of the vaccination programme is well established, with more than 42.5 million doses of H1N1 vaccines administered across Europe (data from Medicines and Healthcare Products Regulatory Agency up to March 2010). Concerns exist regarding vaccination in the immunocompromised host but studies of children undergoing immunomodulatory therapy demonstrate that the vaccine is well tolerated.4 In addition, solid organ transplant patients appear to tolerate vaccination well despite initial concerns that the activation of non-specific cellular immunity might trigger organ rejection.5 Smaller vaccination responses may occur, but it has been demonstrated that the immunocompromised population can still achieve sufficient antibody titres and a second influenza vaccine dose may be given to ensure an adequate response.6 These safety and efficacy data suggest that implementing a vaccination programme in all high-risk patients on admission to hospital should be considered. Serological testing is unfortunately inaccurate as there is an absence of cross-reactivity between influenza strains and interpretation of results is challenging particularly in the immunocompromised population.7,8 A serological testing programme would therefore not be of use when deciding which patients should receive a second vaccine dose. Healthcare workers are a potential source of A(H1N1) nosocomial infection. Research indicates that healthcare workers often continue working during influenza infections, especially if symptoms are mild, and they risk transmitting the virus to their patients.9 Data from the Department of Health indicate that only 30% of frontline healthcare workers at CUH NHS Trust received the seasonal influenza vaccine in winter 2010/11. Mandatory vaccination programmes have been the most effective means of increasing vaccination rates in healthcare workers but the UK has chosen so far not to adopt this approach.10 Limitations of this study include being performed in a single centre with a small population sample and that the impact on the duration of hospital admission could not be assessed. Restricting the incubation period to five days or more may also have missed some cases of HA-A(H1N1). This study should prompt more research into prevention of transmission in vulnerable patients. Visiting restrictions and staff vaccination may reduce in-hospital transmission. Further data are needed to assess the effectiveness of in-hospital vaccination against A(H1N1) and the use of additional doses of vaccine in vulnerable patients. In conclusion, HA-A(H1N1) infection is a common entity accounting for more than 10% of all inpatient cases of A(H1N1)
205
influenza. Care should be taken to identify the ‘at-risk’ population and further studies are required to define the potential role and effectiveness of vaccination in preventing such infection.
Acknowledgements We thank Mrs Bushen and Dr E.F. Wallin for help with data acquisition. Conflict of interest statement None declared. Funding sources Dr T. Veenith is supported by National Institute of Academic Anaesthesia on a Clinical Research Training Fellowship, and Raymond and Beverly Sackler studentship.
References 1. Miller RR, Markewitz BA, Rolfs RT, et al. Clinical findings and demographic factors associated with ICU admission in Utah due to novel 2009 influenza A(H1N1) infection. Chest 2010;137:752e758. 2. Simonds AK, Hanak A, Chatwin M, et al. Evaluation of droplet dispersion during non-invasive ventilation, oxygen therapy, nebuliser treatment and chest physiotherapy in clinical practice: implications for management of pandemic influenza and other airborne infections. Health Technol Assessmnt 2010;14:131e172. 3. Girard M, Tam J, Assossou O, Kieny M. The 2009 A (H1N1) influenza virus pandemic: a review. Vaccine 2010;28:4895e4902. 4. Esposito S, Cecinati V, Russo FG, Principi N. Influenza vaccination in children with cancer receiving chemotherapy. Hum Vaccin 2009;5:430e432. 5. Torii Y, Kimura H, Ochi N, et al. Immunogenicity of inactivated 2009 H1N1 influenza vaccine in pediatric liver transplant recipients. Vaccine 2011;29:4187e4189. 6. Pollyea DA, Brown JMY, Horning SJ. Utility of influenza vaccination for oncology patients. J Clin Oncol 2010;28:2481e2490. 7. Kunisaki KM, Janoff EN. Influenza in immunosuppressed populations: a review of infection frequency, morbidity, mortality, and vaccine responses. Lancet Infect Dis 2009;9:493e504. 8. McVernon J, Laurie K, Barr I, Kelso A, Skeljo M, Nolan T. Absence of cross-reactive antibodies to influenza A (H1N1) 2009 before and after vaccination with 2009 Southern Hemisphere seasonal trivalent influenza vaccine in children aged 6 monthse9 years: a prospective study. Influenza Other Respir Viruses 2011;5:7e11. 9. Elder AG, O’Donnell B, McCruden EA, Symington IS, Carman WF. Incidence and recall of influenza in a cohort of Glasgow healthcare workers during the 1993e4 epidemic: results of serum testing and questionnaire. BMJ 1996;313:1241e1242. 10. Babcock HM, Gemeinhart N, Jones M, Dunagan WC, Woeltje KF. Mandatory influenza vaccination of health care workers: translating policy to practice. Clin Infect Dis 2010;50:459e464.