Although relatively few studies have systematically evaluated the influence of genetic polymorphisms on susceptibility and disease severity in zoonotic H1N1 and H5N1 infections, the data available suggest that host immunogenetic variation could play an important role in determining the outcome of the immune response. With improvements in surveillance and case confirmation as well as new sequencing and gene expression platforms, we now have the capability to study host genetic variants among severe respiratory illness cases. Although several challenges to conducting such a study include ethical permission to carry out genetic polymorphism studies, the need for large numbers of wellcharacterised clinical specimens with relevant clinical data, difficulty to obtain sufficient number of samples from severe and fatal cases at a single institution, and difficulty in identifying mild controls. The extreme cases of human H5N1 disease are very rare, sporadic, with scattered cases in different countries, adding economic and political sensitivities associated with this disease. Overcoming these barriers and conducting collaborative research can lead to insights that will shed light on the varying degree of susceptibility observed between populations during the recent H1N1 pandemic and will provide greater insight into the hostpathogen interactions that determine disease course during severe H5N1 infection. In China, Students in Crowded Dormitories with a Low Ventilation Rate Have More Common Colds: Evidence for Airborne Transmission OBJECTIVE: To test whether the incidence of common colds among college students in China is associated with ventilation rates and crowdedness in dormitories. METHODS: In Phase I of the study, a cross-sectional study, 3712 students living in 1569 dorm rooms in 13 buildings responded to a questionnaire about incidence and duration of common colds in the previous 12 months. In Phase II, air temperature, relative humidity and CO(2) concentration were measured for 24 hours in 238 dorm rooms in 13 buildings, during both summer and winter. Out-to indoor air flow rates at night were calculated based on measured CO(2) concentrations. RESULTS: In Phase I, 10% of college students reported an incidence of more than 6 common colds in the previous 12 months, and 15% reported that each infection usually lasted for more than 2 weeks. Students in 6-person dorm rooms were about 2 times as likely to have an incidence of common colds ≥6 times per year and a duration ≥2 weeks, compared to students in 3-person rooms. In Phase II, 90% of the measured dorm rooms had an out-to indoor air flow rate less than the Chinese standard of 8.3 L/s per person during the heating season. There was a dose-response relationship between out-to indoor air flow rate per person in dorm rooms and the proportion of occupants with annual common cold infections ≥6 times. A mean ventilation rate of 5 L/(s•person) in dorm buildings was associated with 5% of self reported common cold ≥6 times, compared to 35% at 1 L/(s•person). CONCLUSION: Crowded dormitories with low out-to indoor airflow rates are associated with more respiratory infections among college students. ''Common cold'' is a conventional term for a mild upper respiratory illness, with symptoms such as nasal blockage and discharge, sneezing, sore throat and cough [1] . Adults typically have 2-5 common colds per year, and children 4-8 colds [2] . Although such infections are often regarded as trivial, the cost to society is large [3] . Rhinoviruses have been associated with 40-65% of ''common colds'' through the year [4] , and up to 80-92% of colds during outbreaks [5] .