Pandemic (H1N1) 2009, Abu Dhabi, United Arab Emirates, May 2009–March 2010

To ascertain characteristics of pandemic (H1N1) 2009 virus infection, we reviewed medical records for all suspected or confirmed cases reported in Abu Dhabi during May 2009–March 2010. Overall case-fatality rate was 1.4/100,000 population. Most patients who died had ≥1 risk factor, and female decedents were considerably younger than male decedents.

vere illness (ILI with signs such as hypotension, dyspnea, tachypnea, abnormal radiographic appearance of the lungs) or patients with mild illness who had risk factors (e.g., pregnancy, age <5 years, chronic disease). All patients who had symptoms of infl uenza but negative test results by PCR for pandemic (H1N1) 2009 or who were not tested were grouped into the ILI category for statistical analysis.
Data was analyzed using PASW Statistics version 18 (SPSS Inc, Chicago, IL, USA). One-way analysis of variance was used to compare differences in mean age between the 3 groups (ILI, confi rmed pandemic [H1N1] 2009 infections, pandemic [H1N1] 2009-associated deaths) and the χ 2 test (2-sided) to compare gender and national origin of patients.
From May 1, 2009, through March 23, 2010, a total of 2,806 patients with confi rmed or suspected pandemic (H1N1) 2009 infection were reported to HAAD. The fi rst ILI case was recorded on May 3; the number of cases peaked in August ( Figure 1). The fi rst laboratory-confi rmed case occurred on May 20, with the fi rst pandemic (H1N1) 2009-associated death on September 1. Laboratory-confi rmed pandemic (H1N1) 2009 cases showed a bimodal distribution, with the fi rst peak in August and the second peak in October ( Figure 1). The lack of a second peak in the ILI group is probably due to the change in testing recommendations issued by HAAD on September 8 (testing only patients with severe illness or with risk factors).
Of Of the 26 decedents, 15 were male; 12 were United Arab Emirate nationals, and 14 were expatriates. Calculating case-fatality rates (CFR) with laboratory-confi rmed cases as the denominator is, in this type of study, inaccurate and misleading. Because not all persons with symptoms seek medical attention or are tested, pandemic (H1N1) 2009-confi rmed cases are likely to be underestimated and CFR, in turn, to be grossly overestimated (6,7). We chose to represent mortality estimates per 100,000 persons because the number of fatal cases and the population are ac-curately known. This information gave an estimated CFR of 1.4 deaths per 100,000 persons. The mean age of decedents was 43.8 years compared with 21.6 years for persons with laboratory-confi rmed pandemic (H1N1) 2009 infection who survived (1-way analysis of variance, p<0.01). The most common initial symptoms were fever, cough, and breathing diffi culty ( Table 2). All patients with pandemic (H1N1) 2009 who died received oseltamivir; however, complete details of antiviral treatment were available for only 21/26 cases. For 20 patients, treatment was started before or on the day of laboratory confi rmation (mean −3.2 days). Mean duration of antiviral treatment was 8.3 days (range 2-28 days). Most (20/26; 77%) patients with pandemic (H1N1) 2009 who died had >1 underlying risk factor (8), most commonly pregnancy, diabetes, malignancy, and hypertension. Twelve decedents each had 1 risk factor, 3 had 2, 3 had 3, and 2 had 4. Mean duration from hospital admission to death was 27.5 days ( Table 2).
Ages of decedents with pandemic (H1N1) 2009 infection differed signifi cantly by gender; female patients were considerably younger (mean 31.5 years) than male patients (mean 52.9 years). Even after excluding pregnant women from the equation (9), female decedents remained significantly younger than male decedents. In contrast, ages of survivors of pandemic (H1N1) 2009 infection did not differ signifi cantly by sex.

Conclusions
In this study from the United Arab Emirates, we report the epidemiologic and clinical features of pandemic (H1N1) 2009 infection in Abu Dhabi. The characteristics are similar to those reported in other parts of the world (10)(11)(12). Children were most at risk for pandemic (H1N1) 2009 infection; older adults (>60 years) appeared to be least affected, probably because of cross-protective immunity from exposure to antigenically related infl uenza viruses earlier in life (13,14). Twenty-six persons died, most of whom were 21-60 years of age (7,10). This number translates to an overall incidence of pandemic (H1N1) 2009-associated death in Abu Dhabi of 1.4/100,000 population, which is relatively low compared with some studies (11,15).
Our fi ndings are subject to limitations. For example, like most epidemiologic studies based on surveillance systems, data are often incomplete, and therefore resulting analysis can be subject to bias. Nonetheless, we believe the aggressive approach implemented by the Abu Dhabi government (e.g., body temperature scans at airports, isolation of persons suspected to have pandemic [H1N1] 2009, tracing of contacts of persons with confi rmed cases, and providing oseltamivir prophylaxis) played an important role, not only in delaying the onset and spread of pandemic (H1N1) 2009, but also in reducing deaths.  12. ‡The exact date of laboratory confirmation of pandemic (H1N1) 2009 and start of oseltamivir treatment was known for only 21 of the 26 patients.