Optimality and robustness in quorum sensing (QS)-mediated regulation of a costly public good enzyme

Bacteria secrete a variety of public good exoproducts into their environment. These exoproducts are typically produced under the control of quorum sensing (QS), a signaling mechanism by which bacteria sense and respond to changes in their density. QS seems to provide an advantageous strategy to regulate these costly but beneficial exoproducts: it delays production until sufficiently high cell density, when the overall benefit of exoproducts outweighs cost of their production. This notion raises several fundamental questions about QS as a general control strategy adopted by bacteria. How much delay is advantageous? Under what conditions does QS-mediated regulation become advantageous? How does this advantage depend on the kinetic properties of QS? How robust is a given QS system to the stochastic events that occur over bacterial lifecycles? To quantitatively address these questions, we engineered a gene circuit in Escherichia coli to control the synthesis and secretion of a costly but beneficial exoenzyme. We show that exoenzyme production is overall advantageous only if initiated at a sufficiently high density. This property sets the potential advantage for QS-mediated regulation when the initial density is low and the growth cycle is sufficiently long compared with the exoenzyme response time. This advantage of QS-mediated regulation is robust to varying initial cell densities and growth durations, and it is particularly striking when bacteria face uncertainty, such as from stochastic dispersal during their lifecycle. We show, however, that, for QS to be optimal, its kinetic properties must be appropriately tuned; this property has implications for antibacterial treatments that target QS.     

A fitness trade-off between local competition and dispersal in Vibrio cholerae biofilms

Bacteria commonly grow in densely populated surface-bound communities, termed biofilms, where they gain benefits including superior access to nutrients and resistance to environmental insults. The secretion of extracellular polymeric substances (EPS), which bind bacterial collectives together, is ubiquitously associated with biofilm formation. It is generally assumed that EPS secretion is a cooperative phenotype that benefits all neighboring cells, but in fact little is known about the competitive and evolutionary dynamics of EPS production. By studying Vibrio cholerae biofilms in microfluidic devices, we show that EPS-producing cells selectively benefit their clonemates and gain a dramatic advantage in competition against an isogenic EPS-deficient strain. However, this advantage carries an ecological cost beyond the energetic requirement for EPS production: EPS-producing cells are impaired for dispersal to new locations. Our study establishes that a fundamental tradeoff between local competition and dispersal exists among bacteria. Furthermore, this tradeoff can be governed by a single phenotype.     

Combinatorial quorum sensing allows bacteria to resolve their social and physical environment

Quorum sensing (QS) is a cell–cell communication system that controls gene expression in many bacterial species, mediated by diffusible signal molecules. Although the intracellular regulatory mechanisms of QS are often well-understood, the functional roles of QS remain controversial. In particular, the use of multiple signals by many bacterial species poses a serious challenge to current functional theories. Here, we address this challenge by showing that bacteria can use multiple QS signals to infer both their social (density) and physical (mass-transfer) environment. Analytical and evolutionary simulation models show that the detection of, and response to, complex social/physical contrasts requires multiple signals with distinct half-lives and combinatorial (nonadditive) responses to signal concentrations. We test these predictions using the opportunistic pathogen Pseudomonas aeruginosa and demonstrate significant differences in signal decay between its two primary signal molecules, as well as diverse combinatorial responses to dual-signal inputs. QS is associated with the control of secreted factors, and we show that secretome genes are preferentially controlled by synergistic “AND-gate” responses to multiple signal inputs, ensuring the effective expression of secreted factors in high-density and low mass-transfer environments. Our results support a new functional hypothesis for the use of multiple signals and, more generally, show that bacteria are capable of combinatorial communication.Bacteria must often make regulatory decisions on the basis of limited information about their external world (1). In many bacteria, these decisions are aided by the secretion and detection of small diffusible molecules, in a process called quorum sensing (QS) (2, 3). QS controls a variety of traits, including pathogen virulence (3) leading to “QS interference” (2–6) emerging as a control strategy for several bacterial pathogens.The mechanisms underlying production, uptake, and response to these signal molecules are well-understood, but relatively little is known about how quorum sensing contributes to bacterial fitness. Put another way, why do bacteria use QS? The classic adaptive interpretation of QS is that cells produce signal molecules to serve as a proxy for cellular density: more signal implying more bacteria (7–10). Others have argued for a “diffusion-sensing” interpretation, with more signal implying lower rates of mass transfer (diffusion or flow) (11). However, low mass transfer and high cellular density both lead to high signal concentrations, and so these two unknowns—information on the social parameter of cellular density and the asocial mass-transfer rate—are inextricably linked when only one signal is used (12, 13). It is possible that a signal molecule can still provide a reliable indicator of the achievable density of a more costly secreted factor (“efficiency sensing”) (13). However, where investigated, the majority of QS-regulated genes encode nonsecreted gene products (14), and QS is known to control an array of traits in various bacteria that are not directly impacted by mass transfer, such as luminescence, conjugation, or type-3 secretion (10). Even among secretion-related phenotypes, accumulation of a single autoinducer cannot reliably predict the dynamics of secreted products differing in rates of mass transfer or chemical decay or in how they interact with the environment to form beneficial compounds. Here, we argue that, by combinatorially responding to multiple signal molecules with the appropriate molecular properties (differing in chemical decay rates), bacteria can potentially infer the properties of their social and physical environment simultaneously (Fig. S1).     

Counterbalancing angiogenic regulatory factors control the rate of cancer progression and survival in a stage-specific manner

Whereas the roles of proangiogenic factors in carcinogenesis are well established, those of endogenous angiogenesis inhibitors (EAIs) remain to be fully elaborated. We investigated the roles of three EAIs during de novo tumorigenesis to further test the angiogenic balance hypothesis, which suggests that blood vessel development in the tumor microenvironment can be governed by a net loss of negative regulators of angiogenesis in addition to the well-established principle of up-regulated angiogenesis inducers. In a mouse model of pancreatic neuroendocrine cancer, administration of endostatin, thrombospondin-1, and tumstatin peptides, as well as deletion of their genes, reveal neoplastic stage-specific effects on angiogenesis, tumor progression, and survival, correlating with endothelial expression of their receptors. Deletion of tumstatin and thrombospondin-1 in mice lacking the p53 tumor suppressor gene leads to increased incidence and reduced latency of angiogenic lymphomas associated with diminished overall survival. The results demonstrate that EAIs are part of a balance mechanism regulating tumor angiogenesis, serving as intrinsic microenvironmental barriers to tumorigenesis.     

Incidence rates and causes of cirrhosis in a Norwegian population

Objective. To investigate the incidence rate and causes of cirrhosis in a Norwegian population. We also sought to assess the degree of underreporting of cirrhosis to the Norwegian Death Registry. Material and methods. All 1264 patients treated at Aker University Hospital in the period January 1999 to March 2004 who were given a diagnosis indicating cirrhosis, chronic liver disease or symptoms possibly attributable to cirrhosis were screened retrospectively. A search of the registry of histological diagnoses at Department of Pathology was also carried out. Based on the results of histological examinations and non-histological criteria, cirrhosis was confirmed in 194 patients. Calculations of the incidence rate of cirrhosis and frequencies of the various etiologies were based on 93 patients living in the catchment area of the hospital. Causes of death were retrieved from the Norwegian Death Registry. Results. The incidence rate of cirrhosis was 134 per million per year. The majority of cases were due to alcoholic liver disease (53%), followed by viral liver disease (12%), various autoimmune liver diseases (12%), hemochromatosis (4%) and non-alcoholic steatohepatitis (NASH) (3%). No etiology was established in 16%, a group with a high prevalence of diabetes mellitus, indicating that some of these cases were possibly caused by NASH. Among 105 deaths in this cohort of 194 cirrhotic patients, the diagnosis of cirrhosis was absent in the Norwegian Death Registry in 30% of cases. Conclusions. The incidence of cirrhosis in Norway is relatively low, with alcohol as the most important etiologic factor. Significant underreporting to the Norwegian Death Registry was observed.     

Spontaneous bacterial peritonitis prevalence in pretransplant patients and its effect on survival and graft loss post-transplant

AIM To investigate the incidence of spontaneous bacterial peritonitis(SBP) in pre-transplant patients and its effect on post transplant mortality and graft failure. METHODS We conducted a retrospective cohort study of patient records from the organ procurement and transplant network data set. Patients were identified by the presence of SBP pre-transplant. Univariate post-transplant survival models were constructed using the Kaplan-Meier technique and multivariate models were constructed using the Cox proportional hazards model. Variables that affected post-transplant graft survival were identified in the SBP population. RESULTS Forty-seven thousand eight hundred and eighty patient records were included in the analysis for both groups, and 1966(4.11%) patients were identified in the data set as having pre-transplant SBP. Patients that had pre-transplant SBP had higher rates of graft loss from recurrent hepatitis C virus(HCV)(3.6% vs 2.0%, P 0.0001), infections leading to graft loss(1.9% vs 1.3%, P = 0.02), primary non-function(4.3% vs 3.0%, P 0.0001) and chronic rejection(1.1% vs 0.7%, P = 0.04). Kaplan-Meier survival analysis showed a statistically significant difference in all-cause survival in patients with a history of SBP vs those without(P 0.0001). Pretransplant history of SBP was independently predictiveof mortality due to recurrent HCV(HR = 1.11, 95%CI: 1.02-1.21, P 0.017) after liver transplantation.CONCLUSION HCV patients prior to the advent of directing acting anti-viral agents had a higher incidence of pre-transplant SBP than other patients on the liver transplant wait list. SBP history pre-transplant resulted in a higher rate of graft loss due to recurrent HCV infection and chronic rejection.     

Negative correlation does not imply a tradeoff between growth and reproduction in California oaks

A tradeoff between growth and reproduction, often inferred from an inverse correlation between these two variables, is a fundamental paradigm of life-history evolution. Oak species provide a unique test of this relationship because different species mature acorns either in the year of pollination or in the year after pollination. This difference allows for an interspecific comparison testing whether the apparent tradeoff is causal or the result of confounding factors influencing growth and reproduction independently. Based on 13 years of data on five California oak species, we found significant negative correlations between radial growth and seed production in the three species that produce acorns the same year in which pollination occurs, but not in two species that mature acorns the year after pollination. Rainfall, which correlates positively with radial growth and correlates negatively with acorn production (based on the year of pollination), appears to be driving this pattern. We conclude that the observed negative correlations are not causal, but rather a consequence of growth and reproduction being dependent, in opposite ways, on environmental conditions. Thus, contrary to the current consensus, growth and reproduction in these species are apparently largely independent of each other. In contrast, tradeoffs between current and future reproduction appear to be much more important in the life-history evolution of these long-lived plants. We also conclude that a negative correlation does not necessarily imply a causal mechanism and should not be used as the only evidence supporting a tradeoff.     

细胞因子与老年重症肺部感染病原菌的关系探讨

目的 探讨细胞因子与老年人重症肺部感染病原菌的关系。方法 对20例健康老年人、79例ICU感染早期、感染控制后的老年重症肺部感染患者空腹采血，酶联免疫吸附（ELISA）法测定样本的白细胞介素2受体（IL-2R）、白细胞介素6（IL-6）、白细胞介素8（IL-8）、肿瘤坏死因子α（TNF-α）及C反应蛋白（CRP）的含量，并行冷凝集试验（CAT）排除支原体感染；同时细菌培养明确病原菌，评价细胞因子与老年重症肺部感染病原菌的关系。结果 血清IL-2R、IL-6、CRP水平革兰阴性菌（G^-）感染组、革兰阳性菌（G^-）感染组、真菌感染组分别为较对照组均明显增高（P〈0．01），差异有统计学意义；而感染组间比较差异无统计学意义（P〉0．05）。G^＋感染组的血清IL-8水平明显低于G^-感染组及真菌感染组（P〈0．01），但与对照组比较，差异无统计学意义（P〉0．05）。G^＋感染组血清TNF-α水平较对照组增高（P〈0．05），但不如G^-感染组、真菌感染组较对照组增高明显（P〈0．01）；G^＋感染组血清TNF-α水平与G^-感染组、真菌感染组比较显著低下（P〈0．05）。结论 老年重症肺部G^＋感染者血清IL-2R、IL-6、CRP显著升高，而TNF-α升高较轻，IL-8降低，G^-感染患者、真菌感染患者血清TNF-α、IL-2R、IL-6、IL-8、CRP均显著升高。老年肺部感染初期血清TNF-α、IL-8水平可以做为早期协助预测病原菌的指标。     

Association between blood pressure and survival over 9 years in a general population aged 85 and older

OBJECTIVES: To investigate the association between blood pressure and mortality in people aged 85 and older. DESIGN: Population-based prospective study with 9-year follow-up. SETTING: Department of Neuroscience and Neurology and Department of Public Health and General Practice, University of Kuopio, and Department of Clinical Neurosciences, Helsinki University Hospital. PARTICIPANTS: Of all 601 people living in the city of Vantaa born before April 1, 1906, whether living at home or in institutions and alive on April 1, 1991, 521 were clinically examined and underwent blood pressure measurement. MEASUREMENTS: Blood pressure was measured using a standardized method in the right arm of the subject after resting for at least 5 minutes. Information on medical history for each participant was verified from a computerized database containing all primary care health records. Death certificates were obtained from the National Register; the collection of death certificates was complete. RESULTS: After adjusting for age, sex, functional status, and coexisting diseases (earlier-diagnosed myocardial infarction, congestive heart failure, dementia, cancer, stroke, or hypertension), low systolic blood pressure (BP) was associated with risk of death. CONCLUSION: Low systolic BP may be partially related to poor general health and poor vitality, but the very old may represent a select group of individuals, and the use of BP-lowering medications needs to be evaluated in this group.     

Male genital size reflects a tradeoff between attracting mates and avoiding predators in two live-bearing fish species

Male genitalia may experience more rapid, divergent evolution than any other animal character, but why? Research during the past several decades has culminated in the view that genital diversification primarily results from postmating sexual selection (e.g., sperm competition or cryptic female choice). However, the potential roles of premating sexual selection (e.g., mate choice) and natural selection have received little attention. We examined the possible importance of these mechanisms by investigating divergence in male genitalia among populations differing in predator regime for two species of live-bearing fish (Gambusia affinis in Texas and Gambusia hubbsi in The Bahamas). When controlled for body size, males exhibited a larger gonopodium (sperm-transfer organ) in predator-free environments than in predatory environments, a trend that persisted across space (multiple populations), time (multiple years), and species. By conducting laboratory experiments with G. affinis, we found that premating sexual selection seems to favor larger male genitalia (females exhibited mating preference for males having larger gonopodia), but natural selection in the presence of predatory fishes seems to favor reduced genital size (larger gonopodium size was associated with reduced burst-swimming performance, an important antipredator behavior). Although postmating sexual selection is widely presumed to be the most important mechanism driving genital diversification, these findings suggest that alternative mechanisms, particularly for organisms that cannot retract their genitalia, may also prove important.     

Incidence and survival of stomach cancer in a high-risk population of Chile

AIM： To study the incidence and survival rate of stomach cancer （SC） and its associated factors in a high risk population in Chile. METHODS： The population-based cancer registry of Valdivia, included in the International Agency for Research on Cancer system, covers 356396 residents of Valdivia province, Southern Chile. We studied all SC cases entered in this Registry during 1998-2002 （529 cases）. Population data came from the Chilean census （2002）. Standardized incidence rates per 100000 inhabitants （SIR） using the world population, cumulative risk of developing cancer before age 75, and rate ratios by sex, age, ethnicity and social factors were estimated. Relative survival （Ederer Ⅱ method） and age-standardized estimates （Brenner method） were calculated. Specific survival rates （Kaplan-Meier） were measured at 3 and 5 years and survival curves were analyzed with the Logrank and Breslow tests. Survival was studied in relation to demographics, clinical presentation, laboratory results and medical management of the cases. Those variables significantly associated with survival were later included in a Cox multivariate model. RESULTS： Between 1998 and 2002, 529 primary gastric cancers occurred in Valdivia （crude incidence rate 29.2 per 100000 inhabitants）. Most cases were male （69.0%）, residents of urban areas （57.5%） and Hispanic （83.2%）, with a low education level （84.5% 〈 8 school years）. SC SIR was higher in men than women （40.8 and 14.8 respectively, P 〈 0.001）, risk factors were low education RR 4.4 （95% CI： 2.9-6.8） and 1.6, （95% CI： 1.1-2.1） for women and men respectively and Mapuche ethnicity only significant for women （RR 2.2, 95% CI： 1.2-3.7）. Of all cases, 76.4% were histologically confirmed, 11.5% had a death certificate only （DCO）, 56.1% were TNM stage Ⅳ; 445 cases （84.1%） were eligible for survival analysis, all completed five years follow-up; 42 remained alive, 392 died of SC and 11 died from other causes. Specific 5-year survival, excluding cases with DCO, was 10.6% （95% CI： 7.7-13.5）; 5-year relative survival rate was 12.3% （95% CI： 9.1-16.1）, men 10.9% （95% CI： 7.4-15.2） and women 16.1% （95% CI： 9.5-24.5）. Five- year specific survival was higher for patients aged 〈 55 years （17.3%）, with intestinal type of cancer （14.6%）, without metastasis （22.2%）, tumor size 〈 4 cm （60.0%）, without lymphatic invasion （77.1%）, only involvement of the mucous membrane （100%）. Statistically significant independent prognostic factors were： TNM staging, diffuse type, metastasis, supraclavicular adenopathy, palpable tumor, and hepatitis or ascites. CONCLUSION： Social determinants are the main risk factors for SC, but not for survival. An advanced clinical stage at consultation is the main cause of poor SC survival.     

Oxidative stress and metabolic syndrome in a Japanese female population

Aim: One of the methods to evaluate oxidative stress in clinical medical settings is the reactive oxygen metabolites (d‐ROMs) test. While metabolic syndrome (MetS) is considered an oxidative condition, the oxidative status in MetS has not been fully examined using this test. The aim of the present study was to investigate the possible association between oxidative stress as evaluated by the d‐ROMs test and the MetS component number, in a Japanese female population. Methods: The serum oxidant capacity (measured by the d‐ROMs test) was cross‐sectionally determined in cardiovascular disease‐free and non‐smoking women who were not taking medications (n= 180; mean age, 60 ± 10 (standard deviation) years). Their MetS state was determined by the National Cholesterol Education Program Adult Treatment Panel recommendations with minor modifications for a Japanese population. Results: Patients with MetS (n= 60, 362 ± 53 CARR U) showed a significantly higher oxidant capacity by d‐ROMs than those without MetS (n= 120, 324 ± 55 CARR U, P < 0.01). Moreover, the significant increase in the oxidant capacity by d‐ROMs was closely associated with an increase in the MetS component number (trend P < 0.01). Conclusions: These results showed a significantly positive association between the oxidant capacity (by d‐ROMs) and the MetS component number in this population. Further studies are required to establish the clinical applications of this test to MetS practice and clarify the biological mechanisms of the observed relationships.     

Association between calcium sensing receptor gene polymorphisms and chronic pancreatitis in a US population： Role of serine protease inhibitor Kazal 1type and alcohol

AIM： To test the hypothesis that calcium sensing receptor （CASR） polymorphisms are associated with chronic pancreatitis （CP）, and to determine whether serine protease inhibitor Kazal 1type （SPINK1） N34S or alcohol are necessary co-factors in its etiology.
METHODS： Initially, 115 subjects with pancreatitis and 66 controls were evaluated, of whom 57 patients and 21 controls were predetermined to carry the high-risk SPINK1 N34S polymorphism. We sequenced CASR gene exons 2, 3, 4, 5 and 7, areas containing the majority of reported polymorphisms and novel mutations. Based on the initial results, we added 223 patients and 239 controls to analyze three common nonsynonymous single nucleotide polymorphisms （SNPs） in exon 7 （A986S, R990G, and Q1011E）.
RESULTS： The CASR exon 7 R990G polyrnorphism was significantly associated with CP （OR, 2.01; 95% CI, 1.12-3.59; P = 0.015）. The association between CASR R990G and CP was stronger in subjects who reported moderate or heavy alcohol consumption （OR, 3.12; 95% CI, 1.14-9.13; P = 0.018）. There was no association between the various CASR genotypes and SPINK1 N34S in pancreatitis. None of the novel CASR polymorphisms reported from Germany and India was detected.
CONCLUSION： Our United States-based study confirmed an association of CASR and CP and for the first time demonstrated that CASR R990G is a significant risk factor for CP. We also conclude that the risk of CP with CASR R990G is increased in subjects with moderate to heavy alcohol consumption.     

Improved survival in myeloma patients: starting to close in on the gap between elderly patients and a matched normal population

The outcome for multiple myeloma patients has improved since the introduction of bortezomib, thalidomide and lenalidomide. However, studies comparing new and conventional treatment include selected patient groups. We investigated consecutive patients (n = 1638) diagnosed in a defined period and compared survival with a gender‐ and age‐matched cohort Swedish population (n = 9 340 682). Median overall survival for non‐high‐dose treated patients was 2·8 years. The use of bortezomib, thalidomide or lenalidomide in first line therapy predicted a significantly longer overall survival (median 4·9 years) compared to conventional treatment (2·3 years). Among non‐high‐dose treated patients receiving at least 2 lines with bortezomib, thalidomide or lenalidomide, 69% and 63% have survived at 3 and 5 years as compared to 48% and 22% with conventional drugs and 88% and 79% in the matched cohort populations, respectively. The median overall survival in high‐dose treated patients was 6·9 years. Of these patients, 84% survived at 3 years and 70% at 5 years as compared to 98% and 95% in the matched cohort population. Overall survival in the best non‐high‐dose treated outcome group is closing the gap with the matched cohort. Upfront use of new drugs is clearly better than waiting until later lines of treatment.     

Genetic disassembly and combinatorial reassembly identify a minimal functional repertoire of type III effectors in Pseudomonas syringae

The virulence of Pseudomonas syringae and many other proteobacterial pathogens is dependent on complex repertoires of effector proteins injected into host cells by type III secretion systems. The 28 well-expressed effector genes in the repertoire of the model pathogen P. syringae pv. tomato DC3000 were deleted to produce polymutant DC3000D28E. Growth of DC3000D28E in Nicotiana benthamiana was symptomless and 4 logs lower than that of DC3000ΔhopQ1-1, which causes disease in this model plant. DC3000D28E seemed functionally effectorless but otherwise WT in diagnostic phenotypes relevant to plant interactions (for example, ability to inject the AvrPto-Cya reporter into N. benthamiana). Various effector genes were integrated by homologous recombination into native loci or by a programmable or random in vivo assembly shuttle (PRIVAS) system into the exchangeable effector locus in the Hrp pathogenicity island of DC3000D28E. The latter method exploited dual adapters and recombination in yeast for efficient assembly of PCR products into programmed or random combinations of multiple effector genes. Native and PRIVAS-mediated integrations were combined to identify a minimal functional repertoire of eight effector genes that restored much of the virulence of DC3000ΔhopQ1-1 in N. benthamiana, revealing a hierarchy in effector function: AvrPtoB acts with priority in suppressing immunity, enabling other effectors to promote further growth (HopM1 and HopE1), chlorosis (HopG1), lesion formation (HopAM1-1), and near full growth and symptom production (AvrE, HopAA1-1, and/or HopN1 functioning synergistically with the previous effectors). DC3000D28E, the PRIVAS method, and minimal functional repertoires provide new resources for probing the plant immune system.     

Outcomes of invasive mechanical ventilation in children and adolescents hospitalized due to status asthmaticus in United States: a population based study

Objective: Current national estimates of and outcomes of Invasive Mechanical Ventilation (MV) in status asthmaticus (SA) are unclear. The objective of this study is to estimate the incidence and outcomes of MV in hospitalized SA children and adolescents. Methods: We used the Nationwide Inpatient Sample (NIS, 2009–2010), the largest all-payer hospital discharge database in United States. All hospitalizations (age ≤21 years) with a primary diagnosis of SA were selected. MV was identified using ICD-9-CM procedure codes. Multivariable regression analyses were used to examine the association between MV and outcomes (Length of Stay (LOS) and Hospital Charges (HC)). Results: Over the study period, of the 250?718 SA hospitalizations, MV was needed for <96?h in 0.37% hospitalizations and 0.18% had MV for ≥96?h. Complications occurred in 12.4% (30?991) of all hospitalizations with pneumonia (10.8%) being the most common. A total of 65 patients died in hospitals (the overall in-hospital mortality [IHM] rate was 0.03%). About 55 of these deaths occurred among those who had MV (4% IHM rate for those receiving MV). The mean LOS and hospital HC included without MV (2.1?d, $11?921) MV <?96?h (4.8?d, $52?201); MV?>?96?h (15.6?d, $200?336). After adjustment for patient/hospital level factors, the need for MV was associated with significantly higher LOS and HC (p?<?0.0001). Those who had MV<96?h (OR?=?2.58, 95% CI?=?1.77–3.77) or MV?≥?96?h (OR?=?6.23, 95% CI?=?3.87–10.03) had higher risk of developing pneumonia. Conclusions: Although MV is infrequently needed in children and adolescents hospitalized for SA (0.55% incidence rate), it is associated with higher IHM rate and significant hospital resource utilization.