Singapore Med J 2011; 52(7) : 475 Original Article Department of Respiratory Medicine, Changi General Hospital, 2 Simei Street 3, Singapore 529889 Siau C, MBBS, MRCP, FAMS Consultant Tee A, MBBS, MRCP, FCCP Consultant Raghuram J, MB BCh BAO, MRCP, FAMS Senior Consultant Department of Medicine Oh HML, MMed, FRCPE, FRCPG Senior Consultant and Associate Professor Department of Endocrinology Au V, MBBS, MMed, MRCP Consultant Department of Gastroenterology Fock KM, FRCP, FACP, FAMS Senior Consultant and Professor Teo EK, MMed, FRCPE, FACP Senior Consultant and Professor Correspondence to: Dr Siau Chuin Tel: (65) 6788 8833 Fax: (65) 67816202 Email: chuin_siau@ cgh.com.sg Influenza A H1N1 (2009): clinical spectrum of disease among adult patients admitted to a regional hospital in Singapore Siau C, Tee A, Au V, Raghuram J, Oh H M L, Fock K M, Teo E K ABSTRACT Introduction: The worldwide spread of Influenza A H1N1 (2009) has proceeded at an unprecedented rate, with the World Health Organization rapidly raising its influenza pandemic alert to phase six. We describe the disease spectrum of H1N1 (2009) to aid the triaging and identification of patients at risk. Methods: This is a retrospective chart review of all confirmed H1N1 (2009) cases admitted to our institution between June and September 2009. Results: The disease severity of the 153 patients studied was classified as mild (n is 75), moderate (n is 55) and severe (n is 23). 81 patients were female. The median age was 26 years. While comorbidities were more prevalent among patients with moderate–severe illness, 47.4 percent reported no pre-existing illness. Presenting complaints of breathlessness, tachycardia, low-pulse oximetry, higher leukocyte counts and C-reactive protein with low albumin levels were more commonly noted in moderate–severe illness (p-value less than 0.001). All patients received oseltamivir at a median of four days from illness onset. 18 required intensive care unit admission, with the majority (94.4 percent) within the first 24 hours of hospitalisation. The overall mortality rate was 4.6 percent. Median lengths of hospitalisation were four and nine days for moderate and severe cases, respectively. Conclusion: While the majority of H1N1 (2009) patients have mild illness, a subgroup can become critically ill. Prior good health is not necessarily a good discriminator against severe illness. The presence of dyspnoea, tachycardia and desaturation at triage should heighten the index of suspicion for H1N1 (2009)-related complications. Keywords: H1N1 (2009), influenza pandemic, influenza-like illness, oseltamivir Singapore Med J 2011; 52(7): 475-480 INTRODUCTION In March 2009, an outbreak of severe pneumonia was reported in conjunction with the isolation of a novel infuenza A H1N1 (2009) virus in Mexico. (1) In the following months, the worldwide spread of H1N1 (2009) proceeded at an unprecedented rate, aided in part by the convenience of global air travel. (2) In response to the threat of an infuenza pandemic, the World Health Organization (WHO) raised its infuenza pandemic alert to phase 6. Since then, more than 213 countries and overseas territories have reported laboratory-confrmed cases of H1N1 (2009), including at least 16,813 fatalities. (3) Singapore frst reported its case of H1N1 (2009) on May 27, 2009, (4) with evidence of community transmission emerging by June 19, 2009. (5) National healthcare policies had to be adapted to the evolving disease epidemiology. The Health Ministry’s pandemic preparedness plan targeted containment during the initial phase of the outbreak. When it became apparent that community transmission was inevitable, measures were adopted to mitigate the extent of the outbreak in the local community. As such, hospital admission criteria for suspected/confrmed H1N1 (2009) cases were amended accordingly between the months of May and September 2009. While some may argue that certain containment measures adopted during this outbreak were too draconian, we believe that it provided a unique opportunity to study the disease spectrum of H1N1 (2009) infection. We feel that this information would allow us to better triage patients at the primary healthcare level and identify patients who are at risk of developing H1N1 (2009)-related complications. In addition, while the concerns of a second wave of H1N1 (2009) cases may seem to have abated in the recent months, (6) we hope that our experience may be benefcial in the planning of expedient healthcare delivery