That we observed a stronger relationship between low-producing MBL genotypes and MRSA infection than between those genotypes and S. aureus infection in general is puzzling. We are unaware of an obvious physiologic explanation for why low MBL would predispose more strongly to infection with methicillin-resistant versus methicillin-sensitive S. aureus. One possibility is that MRSA is a marker for other strain characteristics. For example, such an association could arise if MRSA infections were predominantly the USA300 strain while other S. aureus infections were predominantly the USA100 strain. Unfortunately, we do not have data on S. aureus genetic strain types. We also found that of the 4 fatal infl uenza cases in which patients had both MRSA co-infection and low-producing MBL genotypes, 2 patients reportedly also had asthma. It is well-established that asthma increases the risk for serious complications of infl uenza, and although we know of no evidence suggesting that low-producing MBL genotypes are associated with increased risk for asthma (40) , this fi nding may be worth further exploration in future studies. Our fi ndings suggest several opportunities for additional infl uenza-related research. An obvious next step is examination of all functional variants of the MBL2 gene in conjunction with gene expression and functional assays in a larger group of severely ill infl uenza case-patients with suffi ciently detailed clinical data to defi ne important phenotypes (e.g., MRSA co-infection). Interest in association studies of rare variants, the availability of new sequencing technologies that dramatically decrease the cost of sequencing, and access to reference human sequence data suggest that investigating rare variants in candidate genes (including MBL2 and TNF) and their functional effects may be a promising avenue of research. Large-scale genotyping of a sample of case-patients to look for common variants by using methods such as genomewide association studies may be possible if a network of collaborators capable of pooling a suffi cient number of case-patients is developed. Recent initiatives such as the Genome-based Research and Population Health International Network (www.graphint. org/ver2) are aimed at encouraging such networks. Given the rapid acceleration in laboratory technologies, enhancement in bioinformatics methods and capacity, and trends toward collaborative research within large consortia, exploration of the role of host genomic factors in serious illness associated with infl uenza and other viral pathogens is increasingly feasible. We believe that host genomics is a promising area for future research regarding who is at risk for severe complications of acute infectious diseases, including infl uenza.  Clinical features and risk factors for severe and critical pregnant women with 2009 pandemic H1N1 influenza infection in China BACKGROUND: 2009 pandemic H1N1 (pH1N1) influenza posed an increased risk of severe illness among pregnant women. Data on risk factors associated with death of pregnant women and neonates with pH1N1 infections are limited outside of developed countries. METHODS: Retrospective observational study in 394 severe or critical pregnant women admitted to a hospital with pH1N1 influenza from Sep. 1, 2009 to Dec. 31, 2009. rRT-PCR testing was used to confirm infection. In-hospital mortality was the primary endpoint of this study. Univariable logistic analysis and multivariate logistic regression analysis were used to investigate the potential factors on admission that might be associated with the maternal and neonatal mortality. RESULTS: 394 pregnant women were included, 286 were infected with pH1N1 in the third trimester. 351 had pneumonia, and 77 died. A PaO(2)/FiO(2 )≤ 200 (odds ratio (OR), 27.16; 95% confidence interval (CI), 2.64-279.70) and higher BMI (i.e. ≥ 30) on admission (OR, 1.26; 95% CI, 1.09 to 1.47) were independent risk factors for maternal death. Of 211 deliveries, 146 neonates survived. Premature delivery (OR, 4.17; 95% CI, 1.19-14.56) was associated neonatal mortality. Among 186 patients who received mechanical ventilation, 83 patients were treated with non-invasive ventilation (NIV) and 38 were successful with NIV. The death rate was lower among patients who initially received NIV than those who were initially intubated (24/83, 28.9% vs 43/87, 49.4%; p = 0.006). Septic shock was an independent risk factor for failure of NIV. CONCLUSIONS: Severe hypoxemia and higher BMI on admission were associated with adverse outcomes for pregnant women. Preterm delivery was a risk factor for neonatal death among pregnant women with pH1N1 influenza infection. NIV may be useful in selected pregnant women without septic shock. Pregnant women are at an increased risk for contracting influenza and its complications associated with influenza [1] . Like previous epidemic and pandemic diseases, 2009 pandemic H1N1 (pH1N1) influenza posed an increased risk of severe illness among pregnant women [2] [3] [4] [5] [6] [7] [8] [9] . A report from the first month of the pH1N1 outbreak noted that the rate of hospitalization among pregnant women was approximately four times the rate in the general population in the USA [3] . As reported by the California Department of Public Health (CDPH), a total of 10% of the 1088 patients who were hospitalized or died from the 2009 pH1N1 influenza were pregnant [10] . According to the Ministry of Health (MOH) of the People's Republic of China, pregnant women accounted for 13.7% of deaths associated with 2009 pH1N1 influenza [11] . Pregnant women with influenza appear to have an increased risk of miscarriage, premature birth and stillbirth [2, 12, 13] . Reports from Victoria in Australia [14, 15] , New York [16] , and California [17] , demonstrate that 2009 pH1N1 infection was associated with substantial maternal and fetal morbidity and mortality. However, information is limited concerning the risk factors for maternal and neonatal death when pregnancy is complicated by severe or critical illness related to 2009 pH1N1 influenza.