Associations between COVID-19 therapies and outcomes in rural and urban America: A multisite, temporal analysis from the Alpha to Omicron SARS-CoV-2 variants.

PURPOSE: To investigate the enduring disparities in adverse COVID-19 events between urban and rural communities in the United States, focusing on the effects of SARS-CoV-2 vaccination and therapeutic advances on patient outcomes. METHODS: Using National COVID Cohort Collaborative (N3C) data from 2021 to 2023, this retrospective cohort study examined COVID-19 hospitalization, inpatient death, and other adverse events. Populations were categorized into urban, urban-adjacent rural (UAR), and nonurban-adjacent rural (NAR). Adjustments included demographics, variant-dominant waves, comorbidities, region, and SARS-CoV-2 treatment and vaccination. Statistical methods included Kaplan-Meier survival estimates, multivariable logistic, and Cox regression. FINDINGS: The study included 3,018,646 patients, with rural residents constituting 506,204. These rural dwellers were older, had more comorbidities, and were less vaccinated than their urban counterparts. Adjusted analyses revealed higher hospitalization odds in UAR and NAR (aOR 1.07 [1.05-1.08] and 1.06 [1.03-1.08]), greater inpatient death hazard (aHR 1.30 [1.26-1.35] UAR and 1.37 [1.30-1.45] NAR), and greater risk of other adverse events compared to urban dwellers. Delta increased, while Omicron decreased, inpatient adverse events relative to pre-Delta, with rural disparities persisting throughout. Treatment effectiveness and vaccination were similarly protective across all cohorts, but dexamethasone post-ventilation was effective only in urban areas. Nirmatrelvir/ritonavir and molnupiravir better protected rural residents against hospitalization. CONCLUSIONS: Despite advancements in treatment and vaccinations, disparities in adverse COVID-19 outcomes persist between urban and rural communities. The effectiveness of some therapeutic agents appears to vary based on rurality, suggesting a nuanced relationship between treatment and geographic location while highlighting the need for targeted rural health care strategies.

Efficacy of 24 hours versus 5 days of prophylactic antibiotics for the prevention of surgical site infection in outpatient elective facial plastic surgery.

Background: The discovery of penicillin marked a paradigm shift in medicine with the ability to treat previously life-threatening infections. Increasing antibiotic resistance as well as the risk of adverse reactions to antibiotics, however, creates pressures for judicious use. There continues to be debate about the role of prophylactic antibiotics in facial plastic surgery. This study explores the role of prophylactic antibiotic administration in elective outpatient facial plastic surgery by comparing 5 days versus 24 hours of antibiotic prophylaxis. Method: A retrospective cohort study of all consecutive patients undergoing cosmetic procedures at an outpatient facial plastic surgical center who received either 5 days or 24 hours of prophylactic antibiotics was performed. The primary outcome was the need for postoperative antibiotics within 6 weeks of surgery. Results: 204 patients met the inclusion criteria: 104 in the 5-day group and 100 in the 24-hour prophylaxis group. The overall infection rate was 3.4%: 3% in the 24-hour group and 3.8% in the 5-day group (p = 0.77). Subgroup analysis of clean-contaminated cases (n = 85) showed the rate of postoperative infections was 4.3%, all within the 5-day group. In clean cases (n = 119), the rate of postoperative infections was 4.2% (n = 5): 4.8% (n = 3) in the 24-hour group versus 3.5% (n = 2) in the 5-day group. Conclusions: The results show that decreasing the duration of antibiotics was not associated with an increased risk of postoperative infection. Given that antibiotics are an increasingly precious commodity with rising rates of resistance, this study supports the use of decreasing postoperative antibiotics to 24 hours.

Hearing Health Awareness and the Need for Educational Outreach Amongst Teachers in Malawi.

Malawi, as a low-income country in southeastern Africa, severely lacks early identification, diagnosis and intervention measures for hearing loss. Due to its constrained resources, an educational awareness campaign targeted at professionals can be a cost-effective instrument in promoting good health care through awareness, prevention, and early identification of hearing loss. The aim of this study is to assess school teachers' knowledge of hearing health, audiology services, identification, and management of hearing issues before and after an educational intervention. METHODS: A Pre-Survey, followed by an educational intervention, and a Post-Survey were completed by teacher participants. A similar World Health Organization-derived survey was also administered to compare to our locally adapted survey. Trends related to efficacy, performance, and survey improvement were evaluated. RESULTS: A total of 387 teachers participated. The average score on the Post-Survey was significantly improved compared to the Pre-Survey (71% to 97% correct responses) with the educational intervention. The only predictive variable related to performance was the location of the school within the capital of Lilongwe compared to rural sites outside of the capital. Our locally adapted survey compared favorably to the WHO survey. CONCLUSIONS: The results suggest that there is a statistically significant improvement in the implementation of an educational program to increase the knowledge and awareness of hearing health care among teachers. Some topics were more poorly understood than others, suggesting the need for targeted awareness interventions. Location within the capital city had some effect on performance but a high rate of correct responses was achievable across the participants independent of age, teaching experience, or gender. Our data support the idea that hearing health awareness interventions can be an effective and low-cost option to equip teachers to effectively serve as an advocate for improved identification, early diagnosis and appropriate referral of students with hearing loss.

Community risks for SARS-CoV-2 infection among fully vaccinated US adults by rurality: A retrospective cohort study from the National COVID Cohort Collaborative.

BACKGROUND: While COVID-19 vaccines reduce adverse outcomes, post-vaccination SARS-CoV-2 infection remains problematic. We sought to identify community factors impacting risk for breakthrough infections (BTI) among fully vaccinated persons by rurality. METHODS: We conducted a retrospective cohort study of US adults sampled between January 1 and December 20, 2021, from the National COVID Cohort Collaborative (N3C). Using Kaplan-Meier and Cox-Proportional Hazards models adjusted for demographic differences and comorbid conditions, we assessed impact of rurality, county vaccine hesitancy, and county vaccination rates on risk of BTI over 180 days following two mRNA COVID-19 vaccinations between January 1 and September 21, 2021. Additionally, Cox Proportional Hazards models assessed the risk of infection among adults without documented vaccinations. We secondarily assessed the odds of hospitalization and adverse COVID-19 events based on vaccination status using multivariable logistic regression during the study period. RESULTS: Our study population included 566,128 vaccinated and 1,724,546 adults without documented vaccination. Among vaccinated persons, rurality was associated with an increased risk of BTI (adjusted hazard ratio [aHR] 1.53, 95% confidence interval [CI] 1.42-1.64, for urban-adjacent rural and 1.65, 1.42-1.91, for nonurban-adjacent rural) compared to urban dwellers. Compared to low vaccine-hesitant counties, higher risks of BTI were associated with medium (1.07, 1.02-1.12) and high (1.33, 1.23-1.43) vaccine-hesitant counties. Compared to counties with high vaccination rates, a higher risk of BTI was associated with dwelling in counties with low vaccination rates (1.34, 1.27-1.43) but not medium vaccination rates (1.00, 0.95-1.07). Community factors were also associated with higher odds of SARS-CoV-2 infection among persons without a documented vaccination. Vaccinated persons with SARS-CoV-2 infection during the study period had significantly lower odds of hospitalization and adverse events across all geographic areas and community exposures. CONCLUSIONS: Our findings suggest that community factors are associated with an increased risk of BTI, particularly in rural areas and counties with high vaccine hesitancy. Communities, such as those in rural and disproportionately vaccine hesitant areas, and certain groups at high risk for adverse breakthrough events, including immunosuppressed/compromised persons, should continue to receive public health focus, targeted interventions, and consistent guidance to help manage community spread as vaccination protection wanes.

HIV specific CD8+ TRM-like cells in tonsils express exhaustive signatures in the absence of natural HIV control.

Lymphoid tissues are an important HIV reservoir site that persists in the face of antiretroviral therapy and natural immunity. Targeting these reservoirs by harnessing the antiviral activity of local tissue-resident memory (TRM) CD8+ T-cells is of great interest, but limited data exist on TRM-like cells within lymph nodes of people living with HIV (PLWH). Here, we studied tonsil CD8+ T-cells obtained from PLWH and uninfected controls from South Africa. We show that these cells are preferentially located outside the germinal centers (GCs), the main reservoir site for HIV, and display a low cytolytic and a transcriptionally TRM-like profile distinct from blood CD8+ T-cells. In PLWH, CD8+ TRM-like cells are expanded and adopt a more cytolytic, activated, and exhausted phenotype not reversed by antiretroviral therapy (ART). This phenotype was enhanced in HIV-specific CD8+ T-cells from tonsils compared to matched blood suggesting a higher antigen burden in tonsils. Single-cell transcriptional and clonotype resolution showed that these HIV-specific CD8+ T-cells in the tonsils express heterogeneous signatures of T-cell activation, clonal expansion, and exhaustion ex-vivo. Interestingly, this signature was absent in a natural HIV controller, who expressed lower PD-1 and CXCR5 levels and reduced transcriptional evidence of T-cell activation, exhaustion, and cytolytic activity. These data provide important insights into lymphoid tissue-derived HIV-specific CD8+ TRM-like phenotypes in settings of HIV remission and highlight their potential for immunotherapy and targeting of the HIV reservoirs.

An ordinal severity scale for COVID-19 retrospective studies using Electronic Health Record data.

Objectives: Although the World Health Organization (WHO) Clinical Progression Scale for COVID-19 is useful in prospective clinical trials, it cannot be effectively used with retrospective Electronic Health Record (EHR) datasets. Modifying the existing WHO Clinical Progression Scale, we developed an ordinal severity scale (OS) and assessed its usefulness in the analyses of COVID-19 patient outcomes using retrospective EHR data. Materials and Methods: An OS was developed to assign COVID-19 disease severity using the Observational Medical Outcomes Partnership common data model within the National COVID Cohort Collaborative (N3C) data enclave. We then evaluated usefulness of the developed OS using heterogenous EHR data from January 2020 to October 2021 submitted to N3C by 63 healthcare organizations across the United States. Principal component analysis (PCA) was employed to characterize changes in disease severity among patients during the 28-day period following COVID-19 diagnosis. Results: The data set used in this analysis consists of 2 880 456 patients. PCA of the day-to-day variation in OS levels over the totality of the 28-day period revealed contrasting patterns of variation in disease severity within the first and second 14 days and illustrated the importance of evaluation over the full 28-day period. Discussion: An OS with well-defined, robust features, based on discrete EHR data elements, is useful for assessments of COVID-19 patient outcomes, providing insights on the progression of COVID-19 disease severity over time. Conclusions: The OS provides a framework that can facilitate better understanding of the course of acute COVID-19, informing clinical decision-making and resource allocation.

The Use of Autologous and Cadaveric Grafts in Rhinoplasty: A Survey Study.

BACKGROUND: Both autologous and cadaveric grafts are often used during rhinoplasty to create volume and provide support. Despite discussion in the literature comparing the efficacy, cost-effectiveness, and complication rates between grafting options, it remains unclear which is the superior choice when considering availability, donor site morbidity, and cost. There is a little description of the current use of these materials amongst facial plastic surgeons. METHODS: A 12 question survey was created, and IRB approval was obtained. The survey was distributed to practicing members of the AAFPRS via their membership listserv. RESULTS: 178 respondents completed the survey for an overall response rate of 17.5%. The most common rhinoplasty graft types used by respondents were autologous septal cartilage (96.6%), autologous auricular grafts (93.8%), autologous rib graft (ARG) (75.8%), and cadaveric rib graft (CRG) (56.7%). Patient comorbidities and performing more than 50 rhinoplasties per year were positively correlated with use of CRG grafts and concerns about complications and cost were negatively correlated. CONCLUSIONS: While autologous septal and auricular cartilage remain the most common graft choices amongst surveyed facial plastic surgeons, a majority utilize cadaveric rib grafts in their practice. Patient comorbidities, surgery volume, concerns about graft complications, and cost were the chief factors associated with use of cadaveric grafts amongst survey respondents. LEVEL OF EVIDENCE V: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Appropriateness of antibiotic use in patients with and without altered mental status diagnosed with a urinary tract infection.

Objective: The objective of this study was to determine antibiotic appropriateness based on Loeb minimum criteria (LMC) in patients with and without altered mental status (AMS). Design: Retrospective, quasi-experimental study assessing pooled data from 3 periods pertaining to the implementation of a UTI management guideline. Setting: Academic medical center in Lexington, Kentucky. Patients: Adult patients aged ≥18 years with a collected urinalysis receiving antimicrobial therapy for a UTI indication. Methods: Appropriateness of UTI management was assessed in patients prior to an institutional UTI guideline, after guideline introduction and education, and after implementation of a prospective audit-and-feedback stewardship intervention from September to November 2017-2019. Patient data were pooled and compared between patients noted to have AMS versus those with classic UTI symptoms. Loeb minimum criteria were used to determine whether UTI diagnosis and treatment was warranted. Results: In total, 600 patients were included in the study. AMS was one of the most common indications for testing across the 3 periods (19%-30.5%). Among those with AMS, 25 patients (16.7%) met LMC, significantly less than the 151 points (33.6%) without AMS (P < .001). Conclusions: Patients with AMS are prescribed antibiotic therapy without symptoms indicative of UTI at a higher rate than those without AMS, according to LMC. Further antimicrobial stewardship efforts should focus on prescriber education and development of clearly defined criteria for patients with and without AMS.

Irreversible depletion of intestinal CD4+ T cells is associated with T cell activation during chronic HIV infection.

HIV infection in the human gastrointestinal (GI) tract is thought to be central to HIV progression, but knowledge of this interaction is primarily limited to cohorts within Westernized countries. Here, we present a large cohort recruited from high HIV endemic areas in South Africa and found that people living with HIV (PLWH) presented at a younger age for investigation in the GI clinic. We identified severe CD4+ T cell depletion in the GI tract, which was greater in the small intestine than in the large intestine and not correlated with years on antiretroviral treatment (ART) or plasma viremia. HIV-p24 staining showed persistent viral expression, particularly in the colon, despite full suppression of plasma viremia. Quantification of mucosal antiretroviral (ARV) drugs revealed no differences in drug penetration between the duodenum and colon. Plasma markers of gut barrier breakdown and immune activation were elevated irrespective of HIV, but peripheral T cell activation was inversely correlated with loss of gut CD4+ T cells in PLWH alone. T cell activation is a strong predictor of HIV progression and independent of plasma viral load, implying that the irreversible loss of GI CD4+ T cells is a key event in the HIV pathogenesis of PLWH in South Africa, yet the underlying mechanisms remain unknown.

Going Global: Interest in Global Health Among US Otolaryngology Residents.

Background: To meet the rising interest in surgical global health, some surgical residency programs offer global health experiences. The level of interest in these programs, however, and their role in residency recruitment and career planning has not been systematically evaluated. Objective: (1) Define interest in global health among Otolaryngology residents in the USA. (2) Assess engagement of Otolaryngology residencies in global health training. (3) Determine barriers to global health training in residency. Methods: A survey questionnaire was developed and sent to all Otolaryngology Residency Program Directors for distribution to all current Otolaryngology residents in the US. Results: A total of 91 complete surveys were collected. A majority of respondents felt that global health was either "very important" or "extremely important" (67%). Two-thirds of respondents had prior global health experience (68%). While 56% of respondents would definitely participate in a global health elective and 78% would likely or definitely participate, only 37% of residency programs offered a global health experience. The availability of a global health elective significantly correlated with residency match choice in respondents with previous global health experience. The three most common barriers to participation were insufficient time, insufficient funding, and lack of program. Conclusion: Participation in bilateral and equitable international electives is a unique experience of personal and professional growth. There is an interest in these opportunities during residency training among Otolaryngology residents that is not reflected in availability within training programs. This suggests the need for development of humanitarian outreach exposure through global health experiences during surgical residency training.

Changing demographics and risk factors for cryptococcosis: A 12-year review at a tertiary care centre.

BACKGROUND: Cryptococcosis is classically associated with the immunocompromised patients but there is a rising appreciation for its impact on the immunocompetent hosts. We sought to analyse the trends, diagnosis, treatment of different hosts and the effect of immunodeficiency and chronic liver disease on relapse and in-house mortality. METHODS: This is a retrospective study of 12 years of patients with cryptococcosis, divided into three different groups: HIV-infected, transplant and non-HIV non-transplant (NHNT). Data were analysed with Chi-square, unpaired parametric t test, simple and multivariate logistic regression analysis. RESULTS: Of 114 identified patients, 23 (20.2%) had HIV infection, 11 (9.6%) had transplant, 80 (70.2%) were NHNT patients. Overall, mortality was 28.1% (32/114) and relapse occurred in 10.5% (12/114) of patients. The mortality trend was higher (OR = 2.346, p = .287) in the transplant group (45.5%, 5/11) than in HIV (26.1%, 6/23) and NHNT groups (26.3%, 21/80). HIV was associated with relapse; 30.4% (7/23) for HIV-positive patients and 5.5% (5/91) for HIV-negative patients (OR = 7.525, p = .002). Chronic liver disease had a large and statistically significant association with mortality on multivariate analysis (OR = 3.583, p = .013) which was more pronounced than the HIV or transplant groups. It was independently associated with mortality by chi-square analysis (OR 3.137, p = .012). CONCLUSION: Chronic liver disease represented 30.7% (35/114) of all studied patients. It was a risk factor for in-hospital mortality. HIV infection and transplant were not statistically significant for mortality. Relapse was highest in the HIV-infected patients at 30.4% (7/23). These data highlight the effect of type and degree of immunocompromise on cryptococcosis.

Assessing the Effectiveness of Cancer Screening Interventions Targeting Appalachian Populations: A Systematic Review.

PURPOSE: Appalachian residents have higher cancer prevalence and invasive cancer incidence in almost all cancer types relative to non-Appalachian residents. Public health interventions have been carried out to increase preventive cancer screening participation. However, no studies have evaluated the effectiveness of existing interventions targeting cancer screening uptake in this high-risk population. The main objective of this study is to assess the effectiveness of interventions aimed at increasing uptake and/or continuing participation in screened cancers (breast, cervical, colorectal, lung, and prostate) in Appalachia. METHODS: We conducted a systematic review of electronic databases and gray literature using a combination of MeSH and free-text search terms related to breast, cervical, colorectal, lung, and prostate cancer; mass screening; health promotion; and Appalachia. We identified 3,014 articles of which 15 articles were included. We assessed methodological quality using validated tools and analyzed findings using narrative synthesis. FINDINGS: Fifteen studies reported uptake and/or continued participation in screening interventions; these focused on cervical (n = 7), colorectal (n = 5), breast (n = 2), and lung (n = 1) cancers in Appalachia. Interventions included diverse components: mass media campaigns, community outreach events, community health workers, interpersonal counseling, and educational materials. We found that multi-strategy interventions had higher screening uptake relative to interventions employing 1 intervention strategy. Studies that targeted noncompliant populations and leveraged existing community-based organization partnerships had a substantial increase in screening participation versus others. CONCLUSIONS: There is an urgent need for further research and implementation of effective cancer prevention and screening interventions to reduce disparities in cancer morbidity and mortality in Appalachian populations.

Cell Cycle Regulation in Macrophages and Susceptibility to HIV-1.

Macrophages are the first line of defence against invading pathogens. They play a crucial role in immunity but also in regeneration and homeostasis. Their remarkable plasticity in their phenotypes and function provides them with the ability to quickly respond to environmental changes and infection. Recent work shows that macrophages undergo cell cycle transition from a G0/terminally differentiated state to a G1 state. This G0-to-G1 transition presents a window of opportunity for HIV-1 infection. Macrophages are an important target for HIV-1 but express high levels of the deoxynucleotide-triphosphate hydrolase SAMHD1, which restricts viral DNA synthesis by decreasing levels of dNTPs. While the G0 state is non-permissive to HIV-1 infection, a G1 state is very permissive to HIV-1 infection. This is because macrophages in a G1 state switch off the antiviral restriction factor SAMHD1 by phosphorylation, thereby allowing productive HIV-1 infection. Here, we explore the macrophage cell cycle and the interplay between its regulation and permissivity to HIV-1 infection.

Plasma IL-5 but Not CXCL13 Correlates With Neutralization Breadth in HIV-Infected Children.

Children may be the optimal target for HIV vaccine development as they generate substantially more frequent and more potent broadly HIV neutralizing antibodies (bnAbs) than adults. Development of a biomarker that correlates with neutralization breadth in this group could function as a powerful tool to facilitate the development of an HIV vaccine. Previously, we observed that this preferential ability in HIV-infected children over adults to generate bnAbs is associated with an enrichment of circulating follicular helper T-cells (TFH) with an effector phenotype, and the presence of IL-21 secreting HIV-specific TFH within lymphoid tissue germinal centers (GC). In adults, bnAbs development has been linked with high plasma levels of CXCL13, a chemoattractant for CXCR5-expressing TFH cells to the lymph node GC. We sought to test this relationship in HIV-infected children, but found no association between neutralization breadth and plasma levels of CXCL13, or with the Th2 cytokines IL-4 and IL-13, or the TFH associated factor Activin A. However, we did find an unexpected association between plasma IL-5 levels and bnAb development in these children. Importantly, although CXCL13 correlated with total circulating TFH cells, it was not associated with effector TFH. Additionally, raised CXCL13 expression was associated with a lower CD4 percentage, higher viral load and a loss of immune function, implying it is associated with progressive disease rather than HIV-specific GC activity in these subjects. Taken together, our data suggests that IL-5 should be evaluated further as a candidate plasma biomarker for HIV neutralization breadth and for monitoring vaccine responses in the pediatric age group.

Transcriptional down-regulation of ccr5 in a subset of HIV+ controllers and their family members.

HIV +Elite and Viremic controllers (EC/VCs) are able to control virus infection, perhaps because of host genetic determinants. We identified 16% (21 of 131) EC/VCs with CD4 +T cells with resistance specific to R5-tropic HIV, reversed after introduction of ccr5. R5 resistance was not observed in macrophages and depended upon the method of T cell activation. CD4 +T cells of these EC/VCs had lower ccr2 and ccr5 RNA levels, reduced CCR2 and CCR5 cell-surface expression, and decreased levels of secreted chemokines. T cells had no changes in chemokine receptor mRNA half-life but instead had lower levels of active transcription of ccr2 and ccr5, despite having more accessible chromatin by ATAC-seq. Other nearby genes were also down-regulated, over a region of ~500 kb on chromosome 3p21. This same R5 resistance phenotype was observed in family members of an index VC, also associated with ccr2/ccr5 down-regulation, suggesting that the phenotype is heritable.

The Role of Routine Culture in the Treatment of Chronic Suppurative Otitis Media: Implications for the Standard of Care in Rural Areas of South Africa.

Chronic Suppurative Otitis Media (CSOM) is a widely prevalent disease, which is a leading cause of acquired deafness worldwide, and is associated with complications with significant mortality and morbidity. It often responds poorly to standard of care therapy and places a disproportionate burden on at-risk populations. The microbiology and antibiotic resistance of CSOM varies based on local factors, including health care access, comorbidities, and antibiotic prescribing practices. We evaluated the role and feasibility of using routine culture for the treatment of CSOM in rural areas as a means of improving treatment of CSOM. More than 400 patients were screened in a rural clinic in South Africa over six weeks, and 14 met study criteria and consented for participation. Gram-negative organisms predominated overall, although Staphylococcus aureus was the most commonly isolated single species. A majority of the pathogens were relatively sensitive to commonly prescribed antibiotics, but two cases of methicillin resistant Staphylococcus aureus were cultured, and one patient grew a Scedosporium species. Treatment on follow-up was able to be directed by culture results, suggesting routine culture at the initial point of contact with the health care system may play a pivotal role in addressing this widely prevalent and devastating disease.

Quantitative comparison of human parainfluenza virus hemagglutinin-neuraminidase receptor binding and receptor cleavage.

The human parainfluenza virus (hPIV) hemagglutinin-neuraminidase (HN) protein binds (H) oligosaccharide receptors that contain N-acetylneuraminic acid (Neu5Ac) and cleaves (N) Neu5Ac from these oligosaccharides. In order to determine if one of HN's two functions is predominant, we measured the affinity of H for its ligands by a solid-phase binding assay with two glycoprotein substrates and by surface plasmon resonance with three monovalent glycans. We compared the dissociation constant (Kd) values from these experiments with previously determined Michaelis-Menten constants (Kms) for the enzyme activity. We found that glycoprotein substrates and monovalent glycans containing Neu5Acα2-3Galß1-4GlcNAc bind HN with Kd values in the 10 to 100 µM range. Km values for HN were previously determined to be on the order of 1 mM (M. M. Tappert, D. F. Smith, and G. M. Air, J. Virol. 85:12146-12159, 2011). A Km value greater than the Kd value indicates that cleavage occurs faster than the dissociation of binding and will dominate under N-permissive conditions. We propose, therefore, that HN is a neuraminidase that can hold its substrate long enough to act as a binding protein. The N activity can therefore regulate binding by reducing virus-receptor interactions when the concentration of receptor is high.

To build a virus on a nucleic acid substrate.

Many viruses package their genomes concomitant with assembly. Here, we show that this reaction can be described by three coefficients: association of capsid protein (CP) to nucleic acid (NA), KNA; CP-CP interaction, ω; and α, proportional to the work required to package NA. The value of α can vary as NA is packaged. A phase diagram of average lnα versus lnω identifies conditions where assembly is likely to fail or succeed. NA morphology can favor (lnα > 0) or impede (lnα < 0) assembly. As lnω becomes larger, capsids become more stable and assembly becomes more cooperative. Where (lnα + lnω) < 0, the CP is unable to contain the NA, so that assembly results in aberrant particles. This phase diagram is consistent with quantitative studies of cowpea chlorotic mottle virus, hepatitis B virus, and simian virus 40 assembling on ssRNA and dsDNA substrates. Thus, the formalism we develop is suitable for describing and predicting behavior of experimental studies of CP assembly on NA.