BACKGROUND: The performance of two piperonyl butoxide (PBO-synergist) insecticide-treated net (ITN) brands, PermaNet(®) 3.0 and Olyset(®) Plus, were evaluated under field conditions in two neighboring districts in Sierra Leone over 36 months to estimate median ITN survival, understand insecticidal efficacy, and identify factors influencing ITN durability. This assessment can help guide future PBO-synergist ITN procurement and replacement strategies. METHODS: This prospective study tracked 370 households and 652 campaign-distributed ITNs from 2020, followed annually for 36 months. Districts were purposefully selected based on shared characteristics. Household surveys were conducted, and 30 ITNs per round were tested for bioefficacy and chemical residue. Key indicators included ITN survival, 24-h mosquito mortality, and chemical content reduction compared to manufacturer targets doses. Cox proportional hazard models identified factors influencing ITN survival. RESULTS: Median useful life was 3.0 (95% CI 2.7-3.5) years for PermaNet(®) 3.0 ITNs in Bo and 2.2 (95% CI 2.0-2.4) years for Olyset(®) Plus ITNs in Moyamba. PermaNet(®) 3.0 ITNs displayed 13% 24-h mortality against pyrethroid-resistant mosquitoes on roof panels, with a 46% reduction in PBO content 34 months post-distribution. Olyset(®) Plus ITNs had 3% f24-hour mortality against pyrethroid-resistant mosquitoes, with a 77% reduction in PBO content. Several factors were associated with improved ITN survival, including cohort ITNs from Bo (adjusted hazard ratio [aHR] = 0.33, p < 0.001), households without children under five (CU5) (aHR = 0.64, p = 0.003), highest socio-economic status tertile (aHR = 0.63, p = 0.016), exposure to social and behaviour change (SBC) messages combined with positive net attitudes (aHR = 0.63, p = 0.008), lack of food storage in sleeping spaces (aHR = 0.56, p = 0.006), exclusive adult use of ITNs (aHR = 0.72, p = 0.048), net folding when not in use (aHR = 0.67, p = 0.015), and drying nets outside (aHR = 0.44, p = 0.008). CONCLUSION: ITNs in Bo outperformed those in Moyamba in both physical and insecticidal performance. However, ITN survival is highly context specific, and further investigation into field performance of new ITN types is necessary across diverse epidemiological settings.

BACKGROUND: Continuous distribution of insecticide treated nets (ITNs) through schools is increasingly utilized by National Malaria Programmes across sub-Saharan Africa to maintain coverage between three-year mass distribution campaigns. In March 2023, the Sierra Leone National Malaria Control Programme (NMCP) piloted its first school-based distribution (SBD) in Kono district, reaching 88,605 pupils in 531 schools with piperonyl butoxide-synergist (PBO) ITNs. The pilot was assessed to determine changes in household and population ITN access and use, and to identify areas where future widescale SBD campaigns in Sierra Leone can be improved. METHODS: This was a mixed methods assessment. A cluster, multi-stage sampled household survey was conducted across 950 households, stratified post-hoc by presence (or not) of children eligible for SBD and powered to determine significant differences in ITN access among 'intervention' households (those with at least one eligible child) and 'control' households (those with no eligible children). Key informant interviews (KIIs) were conducted with 26 SBD stakeholders representing government, donors, third party logistics agencies and implementing partners. RESULTS: One- to two-months post SBD, a significantly higher proportion of households in the intervention group owned at least one ITN (93% versus 69%, p < 0.001) and at least one ITN per two people (42% versus 24%, p < 0.001). Population ITN access was significantly higher in the intervention group than the control group (69% versus 46%, p < 0.001). A higher proportion of the population also reported using an ITN the previous night in the intervention group (71%) than the control group (49%) (p < 0.001). KIIs highlighted resolvable challenges, particularly those related to untimely or insufficient funding, which led to subsequent issues for coordination, storage, transportation, quantification, distribution, training, microplanning and supervision. CONCLUSION: Sierra Leone's SBD pilot significantly improved key ITN ownership, use and access indicators at the household and population levels in Kono district one- to two-months post-SBD. However, intervention population ITN use, and access were still below the NMCP's 80% target. Gaps should be addressed for SBD scale-up. Research on costing, sustained levels of ITN use and access, and the effect of SBD ITNs on malaria parasitaemia may be considered by the NMCP.

BACKGROUND: Malaria transmission in Sierra Leone is intense and perennial, accounting for 40% of clinical consultations. Medical workers diagnose suspected malaria cases using rapid diagnostic tests (RDT) and microscopy, with facility-level results reported to the Health Management Information System (HMIS) as monthly aggregates. Commodity stocks are reported to the Logistics Management Information System (LMIS). Partners investigated a striking increase in confirmed malaria during May-July 2023 in Sierra Leone, peaking in June to 46% above the June 2018-2022 mean. METHODS: The team first analysed national, district, and facility HMIS/LMIS data for RDT stocks, testing rates, and confirmed cases during January 2018-October 2023. Epidemic thresholds, defined as case counts two standard deviations (σ) above the previous 5 years' monthly mean, were assessed. Then four facilities in two districts were visited to interview staff. Lastly, the team reanalysed LMIS RDT stock data for all facilities in Sierra Leone using R to categorize their stock status by month. RESULTS: National epidemic thresholds were surpassed in May (2.56σ) and June (4.81σ) 2023. Twelve of sixteen districts surpassed epidemic thresholds during May-June. Investigation revealed inconsistent RDT distribution to facilities over time. National RDT distribution spiked in May 2023, when 551,888 RDT test kits were delivered. This was substantially larger than the 2019-2022 mean for May (53,121, 1,000% increase) and all months (126,866, 435% increase). Subsequently in June 2023, 386,343 tests were performed, 36% higher than the June 2018-2022 mean (285,123). Staff at all four visited facilities reported recurrent RDT stockouts. The proportion of facilities in Sierra Leone reporting positive RDT stocks at both the start and end of the month increased from 14% in April to 74% in June. 51% of facilities began May with RDT stockout and received RDTs that month. CONCLUSIONS: The 2023 spike in confirmed malaria was likely related to increased testing following an unusually large distribution of RDTs. Fluctuations in RDT availability impede the ability to recognize true case variations. Sierra Leone and its partners can strengthen supply chain logistics and health commodity stock tracking to ensure a consistent supply of RDTs and improve interpretation of surveillance data.

BACKGROUND: Information on the status of insecticide resistance in malaria vectors is critical for implementing effective malaria vector control. The Sierra Leone National Malaria Control Programme, in collaboration with the PMI VectorLink project, assessed the resistance status to insecticides commonly used in public health, and associated resistance mechanisms in Anopheles gambiae, the main vector of malaria in Sierra Leone. METHODS: The susceptibility of An. gambiae against pyrethroids with and without piperonyl butoxide (PBO), chlorfenapyr, clothianidin, bendiocarb and pirimiphos-methyl was evaluated in four districts of Sierra Leone in 2018 and 2019 using WHO and CDC bottle bioassay protocols. A subset of samples that were exposed to the insecticides were screened for molecular markers of insecticide resistance, knock-down resistance (kdr) L1014F, 1014S and N1575Y, and (ace-1-G119S). RESULTS: Anopheles gambiae from all sites were resistant to the diagnostic doses of three pyrethroids: deltamethrin, permethrin and alpha-cypermethrin. Intensity of resistance to all three pyrethroids was high, with less than 95% mortality at 10X concentration. However, pre-exposure of An. gambiae to PBO increased overall mortality by 41.6%, 50.0% and 44.0% for deltamethrin, permethrin and alpha-cypermethrin, respectively. The vector was susceptible to chlorfenapyr, clothianidin and pirimiphos-methyl, while bendiocarb showed possible resistance. The frequency of kdr alleles was 98.2% for L1014F, 2.1% for 1014S and 8.9% for N1575Y, while the frequency of the Ace-1 G119S allele was 13.6%. Significant deviation from the Hardy-Weinberg equilibrium and deficiency of heterozygotes was detected only at the G119S locus of An. gambiae (p < 0.0001). Of the 191 An. gambiae sensu lato that were molecularly identified to the species level, 81.7% were An. gambiae sensu stricto (95% CI 75.3-86.7), followed by Anopheles coluzzii (17.8%, 95% CI (12.8-24.1) with one hybrid of An. gambiae/An. coluzzii 0.5%, 95% CI (0.03-3.3). CONCLUSION: Malaria vectors were highly resistant to pyrethroids but exposure to PBO partially restored susceptibility in An. gambiae s.l. in Sierra Leone. Malaria vectors were susceptible to chlorfenapyr, clothianidin and pirimiphos-methyl with possible resistance to bendiocarb. These data informed the selection and distribution of ITN PBO in Sierra Leone's mass campaigns in 2020 and selection of clothianidin for indoor residual spraying in 2021.

Studies among men who have sex with men (MSM) in sub-Saharan Africa (SSA) focus mainly on HIV epidemiology, revealing little about the diversity within this population. We utilized data from the HIV Prevention Trials Network (HPTN) 075 study, to explore demographic and psychosexual characteristics of MSM in SSA who also have sex with women. Persons included in the analyses were aged 18-44 years and assigned male sex at birth and identified as male, reported anal sex with a man in the past 3 months, and had enrolled at one of four study sites (Kisumu, Kenya; Blantyre, Malawi; Cape Town and Soweto, South Africa). Nearly a quarter of the participants had recently engaged in sex with both men and women (MSMW). These men differed in terms of demographic and psychosexual characteristics, and sexual behavior from men who only had had sex with men (MSME). Compared to the latter, MSMW were more likely to prefer the insertive sexual role, reported more sexual partners in the past three months, and had more instances of condomless insertive anal intercourse with a man. These findings suggest that men who have sex with both men and women have specific characteristics and need tailored interventions that take their specific needs into account.

BACKGROUND: Malaria remains a major cause of morbidity and mortality in sub-Saharan Africa. Using insecticide-treated nets (ITNs) every night, year-round is critical to maximize protection against malaria. This study describes sociodemographic, psychosocial, and household factors associated with consistent ITN use in Cameroon, Côte d'Ivoire and Sierra Leone. METHODS: Cross-sectional household surveys employed similar sampling procedures, data collection tools, and methods in three countries. The survey sample was nationally representative in Côte d'Ivoire, representative of the North and Far North regions in Cameroon, and representative of Bo and Port Loko districts in Sierra Leone. Analysis used multilevel logistic regression and sociodemographic, ideational, and household independent variables among households with at least one ITN to identify correlates of consistent ITN use, defined as sleeping under an ITN every night the preceding week. FINDINGS: Consistent ITN use in Côte d'Ivoire was 65.4%, 72.6% in Cameroon, and 77.1% in Sierra Leone. While several sociodemographic and ideational variables were correlated with consistent ITN use, these varied across countries. Multilevel logistic regression results showed perceived self-efficacy to use ITNs and positive attitudes towards ITN use were variables associated with consistent use in all three countries. The perception of ITN use as a community norm was positively linked with consistent use in Cameroon and Côte d'Ivoire but was not significant in Sierra Leone. Perceived vulnerability to malaria was positively linked with consistent use in Cameroon and Sierra Leone but negatively correlated with the outcome in Côte d'Ivoire. Household net sufficiency was strongly and positively associated with consistent use in all three countries. Finally, the findings revealed strong clustering at the household and enumeration area (EA) levels, suggesting similarities in net use among respondents of the same EA and in the same household. CONCLUSIONS: There are similarities and differences in the variables associated with consistent ITN use across the three countries and several ideational variables are significant. The findings suggest that a social and behaviour change strategy based on the ideation model is relevant for increasing consistent ITN use and can inform specific strategies for each context. Finally, ensuring household net sufficiency is essential.

On July 18, 2022, the New York State Department of Health (NYSDOH) notified CDC of detection of poliovirus type 2 in stool specimens from an unvaccinated immunocompetent young adult from Rockland County, New York, who was experiencing acute flaccid weakness. The patient initially experienced fever, neck stiffness, gastrointestinal symptoms, and limb weakness. The patient was hospitalized with possible acute flaccid myelitis (AFM). Vaccine-derived poliovirus type 2 (VDPV2) was detected in stool specimens obtained on days 11 and 12 after initial symptom onset. To date, related Sabin-like type 2 polioviruses have been detected in wastewater* in the patient's county of residence and in neighboring Orange County up to 25 days before (from samples originally collected for SARS-CoV-2 wastewater monitoring) and 41 days after the patient's symptom onset. The last U.S. case of polio caused by wild poliovirus occurred in 1979, and the World Health Organization Region of the Americas was declared polio-free in 1994. This report describes the second identification of community transmission of poliovirus in the United States since 1979; the previous instance, in 2005, was a type 1 VDPV (1). The occurrence of this case, combined with the identification of poliovirus in wastewater in neighboring Orange County, underscores the importance of maintaining high vaccination coverage to prevent paralytic polio in persons of all ages.

INTRODUCTION: Men who have sex with men (MSM) and transgender women (TGW) in sub-Saharan Africa (SSA) are profoundly affected by HIV with high HIV prevalence and incidence. This population also faces strong social stigma and legal barriers, potentially impeding participation in research. To date, few multi-country longitudinal HIV research studies with MSM/TGW have been conducted in SSA. Primary objective of the HIV Prevention Trials Network (HPTN) 075 study was to assess feasibility of recruiting and retaining a multinational prospective cohort of MSM/TGW in SSA for HIV prevention research. METHODS: HPTN 075, conducted from 2015 to 2017, was designed to enroll 400 MSM/TGW at four sites in SSA (100 per site: Kisumu, Kenya; Blantyre, Malawi; Cape Town, South Africa; and Soweto, South Africa). The number of HIV-positive persons was capped at 20 per site; HIV-positive persons already in care were excluded from participation. The one-year study included five biobehavioural assessments. Community-based input and risk mitigation protocols were included in study design and conduct. RESULTS: Of 624 persons screened, 401 were enrolled. One in five participants was classified as transgender. Main reasons for ineligibility included: (a) being HIV positive after the cap was reached (29.6%); (b) not reporting anal intercourse with a man in the preceding three months (20.6%); and (c) being HIV positive and already in care (17.5%). Five (1.2%) participants died during the study (unrelated to study participation). 92.9% of the eligible participants (368/396) completed the final study visit and 86.1% participated in all visits. The main, overlapping reasons for early termination included being (a) unable to adhere to the visit schedule, predominantly because of relocation (46.4%), and (b) unable to contact the participant (32.1%). Participants reported strong motivation to participate and few participation barriers. Four participants reported social harms (loss of confidentiality and sexual harassment by study staff) that were successfully addressed. CONCLUSIONS: HPTN 075 successfully enrolled a multinational sample of MSM/TGW in SSA in a prospective HIV prevention research study with a high retention rate and few documented social harms. This supports the feasibility of conducting large-scale research trials in this population to address its urgent, unmet HIV prevention needs.

ABSTRACT The inability to access health services when needed is a critical barrier to HIV prevention, treatment and care among men who have sex with men (MSM) and transgender women (TGW). Using data collected in HPTN 075, we explored factors associated with any experienced healthcare-related stigma. HPTN 075 was a cohort study to assess the feasibility of recruiting and retaining MSM and TGW in clinical trials in sub-Saharan Africa. Of 401 MSM and TGW enrolled at four sites (Kisumu, Kenya; Blantyre, Malawi; Cape Town, Soweto, South Africa) 397 contributed to the analysis (79.9% cis-gender and 20.1% TGW). Of these, (45.3%; 180/397) reported one or more of healthcare-related stigma experiences. Most frequently reported experiences included fear to seek healthcare services (36.3%) and avoiding seeking such services because of the discovery of MSM status (29.2%). Few men and TGW (2.5%) reported having been denied health services because of having sex with men. In multivariable analysis, more participants in Soweto [adjusted odds ratio (AOR) = 2.60] and fewer participants in Blantyre (AOR = 0.27) reported any healthcare-related stigma experiences, in comparison to participants in Kisumu. MSM and TGW that did not have a supportive gay community to rely on were more likely to report any healthcare-related stigma experiences (AOR = 1.46), whereas MSM and TGW who reported high social support and who never had engaged in transactional sex were less likely to report such experiences (AOR = 0.76 and AOR = 0.43, respectively). Our results suggest that encouraging support groups for MSM and TGW as well as training and sensitizing healthcare staff, and the general community, on MSM and TGW health issues and cultural competence may reduce stigma, improve access to healthcare, which could ultimately reduce HIV transmission.

During 2013, the Maryland Department of Health and Mental Hygiene in Baltimore, MD, USA, received report of 2 Maryland residents whose surgical sites were infected with rapidly growing mycobacteria after cosmetic procedures at a clinic (clinic A) in the Dominican Republic. A multistate investigation was initiated; a probable case was defined as a surgical site infection unresponsive to therapy in a patient who had undergone cosmetic surgery in the Dominican Republic. We identified 21 case-patients in 6 states who had surgery in 1 of 5 Dominican Republic clinics; 13 (62%) had surgery at clinic A. Isolates from 12 (92%) of those patients were culture-positive for Mycobacterium abscessus complex. Of 9 clinic A case-patients with available data, all required therapeutic surgical intervention, 8 (92%) were hospitalized, and 7 (78%) required ≥3 months of antibacterial drug therapy. Healthcare providers should consider infection with rapidly growing mycobacteria in patients who have surgical site infections unresponsive to standard treatment.

We conducted prospective, community-wide surveillance for acute respiratory illnesses (ARIs) in Rochester, NY and Marshfield, WI during a 3-month period in winter 2011. We estimated the incidence of ARIs in each community, tested for viruses, and determined the proportion of ARIs associated with healthcare visits. We used a rolling cross-sectional design to sample participants, conducted telephone interviews to assess ARI symptoms (defined as a current illness with feverishness or cough within the past 7 days), collected nasal/throat swabs to identify viruses, and extracted healthcare utilization from outpatient/inpatient records. Of 6492 individuals, 321 reported an ARI within 7 days (4.9% total, 5.7% in Rochester, 4.4% in Marshfield); swabs were collected from 208 subjects. The cumulative ARI incidence for the entire 3-month period was 52% in Rochester [95% confidence interval (CI) 42-63] and 35% in Marshfield (95% CI 28-42). A specific virus was identified in 39% of specimens: human coronavirus (13% of samples), rhinovirus (12%), RSV (7%), influenza virus (4%), human metapneumovirus (4%), and adenovirus (1%). Only 39/200 (20%) had a healthcare visit (2/9 individuals with influenza). ARI incidence was ~5% per week during winter.

In August 2013, the Maryland Department of Health and Mental Hygiene (MDHMH) was notified of two persons with rapidly growing nontuberculous mycobacterial (RG-NTM) surgical-site infections. Both patients had undergone surgical procedures as medical tourists at the same private surgical clinic (clinic A) in the Dominican Republic the previous month. Within 7 days of returning to the United States, both sought care for symptoms that included surgical wound abscesses, clear fluid drainage, pain, and fever. Initial antibiotic therapy was ineffective. Material collected from both patients' wounds grew Mycobacterium abscessus exhibiting a high degree of antibiotic resistance characteristic of this organism.

Biodiversity and relative abundance of ticks and associated arboviruses in Garissa (northeastern) and Isiolo (eastern) provinces of Kenya were evaluated. Ticks were collected from livestock, identified to species, pooled, and processed for virus isolation. In Garissa, Rhipicephalus pulchellus Gerstacker (57.8%) and Hyalomma truncatum Koch (27.8%) were the most abundant species sampled, whereas R. pulchellus (80.4%) and Amblyomma gemma Donitz (9.6%) were the most abundant in Isiolo. Forty-four virus isolates, comprising Dugbe virus (DUGV; n = 22) and Kupe virus (n = 10; Bunyaviridae: Nirovirus), Dhori virus (DHOV; n = 10; Orthomyxoviridae: Thogotovirus), and Ngari virus (NRIV; n = 2; Bunyaviridae: Orthobunyavirus), were recovered mostly from R. pulchellus sampled in Isiolo. DUGV was mostly recovered from R. pulchellus from sheep and cattle, and DHOV from R. pulchellus from sheep. All Kupe virus isolates were from Isiolo ticks, including R. pulchellus from all the livestock, A. gemma and Amblyomma variegatum F. from cattle, and H. truncatum from goat. NRIV was obtained from R. pulchellus and A. gemma sampled from cattle in Isiolo and Garissa, respectively, while all DHOV and most DUGV (n = 12) were from R. pulchellus sampled from cattle in Garissa. DUGV was also recovered from H. truncatum and Amblyomma hebraeum Koch from cattle and from Rhipicephalus annulatus Say from camel. This surveillance study has demonstrated the circulation of select tick-borne viruses in parts of eastern and northeastern provinces of Kenya, some of which are of public health importance. The isolation of NRIV from ticks is particularly significant because it is usually known to be a mosquito-borne virus affecting humans.

We estimated Rift Valley fever (RVF) incidence as a function of geological, geographical, and climatological factors during the 2006-2007 RVF epidemic in Kenya. Location information was obtained for 214 of 340 (63%) confirmed and probable RVF cases that occurred during an outbreak from November 1, 2006 to February 28, 2007. Locations with subtypes of solonetz, calcisols, solonchaks, and planosols soil types were highly associated with RVF occurrence during the outbreak period. Increased rainfall and higher greenness measures before the outbreak were associated with increased risk. RVF was more likely to occur on plains, in densely bushed areas, at lower elevations, and in the Somalia acacia ecological zone. Cases occurred in three spatial temporal clusters that differed by the date of associated rainfall, soil type, and land usage.

As part of ongoing arbovirus surveillance, we screened ticks obtained from livestock in northeastern Kenya in 2008 to assess the risk for human exposure to tick-borne viruses. Of 1,144 pools of 8,600 Hyalomma spp. ticks screened for Congo-Crimean hemorrhagic fever virus by reverse transcription PCR, 23 pools were infected, demonstrating a potential for human exposure.

In December 2006, Rift Valley fever (RVF) was diagnosed in humans in Garissa Hospital, Kenya and an outbreak reported affecting 11 districts. Entomologic surveillance was performed in four districts to determine the epidemic/epizootic vectors of RVF virus (RVFV). Approximately 297,000 mosquitoes were collected, 164,626 identified to species, 72,058 sorted into 3,003 pools and tested for RVFV by reverse transcription-polymerase chain reaction. Seventy-seven pools representing 10 species tested positive for RVFV, including Aedes mcintoshi/circumluteolus (26 pools), Aedes ochraceus (23 pools), Mansonia uniformis (15 pools); Culex poicilipes, Culex bitaeniorhynchus (3 pools each); Anopheles squamosus, Mansonia africana (2 pools each); Culex quinquefasciatus, Culex univittatus, Aedes pembaensis (1 pool each). Positive Ae. pembaensis, Cx. univittatus, and Cx. bitaeniorhynchus was a first time observation. Species composition, densities, and infection varied among districts supporting hypothesis that different mosquito species serve as epizootic/epidemic vectors of RVFV in diverse ecologies, creating a complex epidemiologic pattern in East Africa.

A large Rift Valley fever (RVF) outbreak occurred in Kenya from December 2006 to March 2007. We conducted a study to define risk factors associated with infection and severe disease. A total of 861 individuals from 424 households were enrolled. Two hundred and two participants (23%) had serologic evidence of acute RVF infection. Of these, 52 (26%) had severe RVF disease characterized by hemorrhagic manifestations or death. Independent risk factors for acute RVF infection were consuming or handling products from sick animals (odds ratio [OR] = 2.53, 95% confidence interval [CI] = 1.78-3.61, population attributable risk percentage [PAR%] = 19%) and being a herds person (OR 1.77, 95% CI = 1.20-2.63, PAR% = 11%). Touching an aborted animal fetus was associated with severe RVF disease (OR = 3.83, 95% CI = 1.68-9.07, PAR% = 14%). Consuming or handling products from sick animals was associated with death (OR = 3.67, 95% CI = 1.07-12.64, PAR% = 47%). Exposures related to animal contact were associated with acute RVF infection, whereas exposures to mosquitoes were not independent risk factors.

Historical outbreaks of Rift Valley fever (RVF) since the early 1950s have been associated with cyclical patterns of the El Nino/Southern Oscillation (ENSO) phenomenon, which results in elevated and widespread rainfall over the RVF endemic areas of Africa. Using satellite measurements of global and regional elevated sea surface temperatures, elevated rainfall, and satellite derived-normalized difference vegetation index data, we predicted with lead times of 2-4 months areas where outbreaks of RVF in humans and animals were expected and occurred in the Horn of Africa, Sudan, and Southern Africa at different time periods from September 2006 to March 2008. Predictions were confirmed by entomological field investigations of virus activity and by reported cases of RVF in human and livestock populations. This represents the first series of prospective predictions of RVF outbreaks and provides a baseline for improved early warning, control, response planning, and mitigation into the future.

An outbreak of Rift Valley fever (RVF) occurred in Kenya during November 2006 through March 2007. We characterized the magnitude of the outbreak through disease surveillance and serosurveys, and investigated contributing factors to enhance strategies for forecasting to prevent or minimize the impact of future outbreaks. Of 700 suspected cases, 392 met probable or confirmed case definitions; demographic data were available for 340 (87%), including 90 (26.4%) deaths. Male cases were more likely to die than females, Case Fatality Rate Ratio 1.8 (95% Confidence Interval [CI] 1.3-3.8). Serosurveys suggested an attack rate up to 13% of residents in heavily affected areas. Genetic sequencing showed high homology among viruses from this and earlier RVF outbreaks. Case areas were more likely than non-case areas to have soil types that retain surface moisture. The outbreak had a devastatingly high case-fatality rate for hospitalized patients. However, there were up to 180,000 infected mildly ill or asymptomatic people within highly affected areas. Soil type data may add specificity to climate-based forecasting models for RVF.