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Disease Outbreaks - Top 30 Publications

Summary of Notifiable Noninfectious Conditions and Disease Outbreaks: Surveillance Data Published Between April 1, 2016 and January 31, 2017 - United States.

The Summary of Notifiable Noninfectious Conditions and Disease Outbreaks: Surveillance Data Published Between April 1, 2016 and January 31, 2017 - United States, herein referred to as the Summary (Noninfectious), contains official statistics for nationally notifiable noninfectious conditions and disease outbreaks. This Summary (Noninfectious) is being published in the same volume of MMWR as the annual Summary of Notifiable Infectious Diseases and Conditions (1). Data on notifiable noninfectious conditions and disease outbreaks from prior years have been published previously (2,3).

Disease surveillance in England and Wales, July 2017.

Current and emerging issues: reminder of the notifiable status of porcine epidemic diarrhoeaHighlights from the scanning surveillance networkUpdate on international disease threatsReview of animal health threats by the Veterinary Risk Group These are among matters discussed in the Animal and Plant Health Agency's (APHA's) disease surveillance report for July 2017.

Notes from the Field: Epidemic Keratoconjunctivitis Outbreak Associated with Human Adenovirus Type 8 - U.S. Virgin Islands, June-November 2016.

On October 11, 2016, the U.S. Virgin Islands Department of Health (USVI DOH) was notified by a local ophthalmologist of an unexpected increase in the number of patients with suspected epidemic keratoconjunctivitis (EKC) during the preceding month. EKC is a severe form of acute conjunctivitis caused by human adenoviruses (HAdVs). Clinical illness typically lasts 1 to 3 weeks and is usually self-limited; treatment is supportive (1). HAdVs can survive for weeks in the environment and are resistant to common disinfectants (2,3). USVI DOH and CDC investigated during October 11-November 29, 2016 to determine the scope of the outbreak, and provide infection control recommendations.

Solid Organ Transplant-Transmitted Tuberculosis Linked to a Community Outbreak - California, 2015.

In the spring of 2015, a local health department (LHD) in county A notified the California Department of Public Health (CDPH) about three adults with close ties to one another and a congregate community site who had received diagnoses of tuberculosis (TB) disease within a 3-month period. Subsequent review revealed matching TB genotypes indicating that the cases were likely part of a chain of TB transmission. Only three TB cases in California in the preceding 2 years shared this same genotype. One of those three previous cases occurred in a lung-transplant recipient who had no identified epidemiologic links to the outbreak. CDPH, multiple LHDs, and CDC conducted an investigation and determined that the lung-transplant donor (patient 1) was epidemiologically linked to the three outbreak cases and had a tuberculin skin test (TST) conversion detected in 2012 upon reentry at a local jail. Three other solid organ recipients from this donor were identified; none had developed TB disease. This investigation suggests that review of organ donors' medical records from high-risk environments, such as jails, might reveal additional information about TB risk. The evaluation of TB in organ recipients could include genotyping analysis (1) and coordination among local, state, and national partners to evaluate the potential for donor-derived TB.

Meningitis Outbreak Caused by Vaccine-Preventable Bacterial Pathogens - Northern Ghana, 2016.

Bacterial meningitis is a severe, acute infection of the fluid surrounding the brain and spinal cord that can rapidly lead to death. Even with recommended antibiotic treatment, up to 25% of infected persons in Africa might experience neurologic sequelae (1). Three regions in northern Ghana (Upper East, Northern, and Upper West), located in the sub-Saharan "meningitis belt" that extends from Senegal to Ethiopia, experienced periodic outbreaks of meningitis before introduction of serogroup A meningococcal conjugate vaccine (MenAfriVac) in 2012 (2,3). During December 9, 2015-February 16, 2016, a total of 432 suspected meningitis cases were reported to health authorities in these three regions. The Ghana Ministry of Health, with assistance from CDC and other partners, tested cerebrospinal fluid (CSF) specimens from 286 patients. In the first 4 weeks of the outbreak, a high percentage of cases were caused by Streptococcus pneumoniae; followed by an increase in cases caused by Neisseria meningitidis, predominantly serogroup W. These data facilitated Ghana's request to the International Coordinating Group* for meningococcal polysaccharide ACW vaccine, which was delivered to persons in the most affected districts. Rapid identification of the etiologic agent causing meningitis outbreaks is critical to inform targeted public health and clinical interventions, including vaccination, clinical management, and contact precautions.

Outbreak of Septic Arthritis Associated with Intra-Articular Injections at an Outpatient Practice - New Jersey, 2017.

On March 6, 2017, the New Jersey Department of Health (NJDOH) was notified of three cases of septic arthritis in patients who had received intra-articular injections for osteoarthritic knee pain at a private outpatient practice. The practice voluntarily closed the next day. NJDOH, in conjunction with the local health department and the New Jersey Board of Medical Examiners, conducted an investigation and identified 41 cases of septic arthritis associated with intra-articular injections administered during 250 patient visits at the same practice, including 30 (73%) patients who required surgery. Bacterial cultures of synovial fluid or tissue from 15 (37%) patients were positive; all recovered organisms were oral flora. An infection prevention assessment of the practice identified multiple breaches of recommended infection prevention practices, including inadequate hand hygiene, inappropriate use of pharmacy bulk packaged (PBP) products as multiple-dose containers and handling PBP products outside of required pharmacy conditions, and preparation of syringes up to 4 days in advance of their intended use. No additional septic arthritis cases were identified after infection prevention recommendations were implemented within the practice.

Wetlands, wild Bovidae species richness and sheep density delineate risk of Rift Valley fever outbreaks in the African continent and Arabian Peninsula.

Rift Valley fever (RVF) is an emerging, vector-borne viral zoonosis that has significantly impacted public health, livestock health and production, and food security over the last three decades across large regions of the African continent and the Arabian Peninsula. The potential for expansion of RVF outbreaks within and beyond the range of previous occurrence is unknown. Despite many large national and international epidemics, the landscape epidemiology of RVF remains obscure, particularly with respect to the ecological roles of wildlife reservoirs and surface water features. The current investigation modeled RVF risk throughout Africa and the Arabian Peninsula as a function of a suite of biotic and abiotic landscape features using machine learning methods. Intermittent wetland, wild Bovidae species richness and sheep density were associated with increased landscape suitability to RVF outbreaks. These results suggest the role of wildlife hosts and distinct hydrogeographic landscapes in RVF virus circulation and subsequent outbreaks may be underestimated. These results await validation by studies employing a deeper, field-based interrogation of potential wildlife hosts within high risk taxa.

Epidemiology, clinical features and risk factors for human rabies and animal bites during an outbreak of rabies in Maputo and Matola cities, Mozambique, 2014: Implications for public health interventions for rabies control.

In Mozambique, the majority of rabies outbreaks are unreported and data on the epidemiological features of human rabies and animal bites are scarce. An outbreak of human rabies in adjacent Maputo and Matola cities in 2014 prompted us to investigate the epidemiology, clinical features and risk factors of human rabies and animal bites in the two cities.

Analysis of patient data from laboratories during the Ebola virus disease outbreak in Liberia, April 2014 to March 2015.

An outbreak of Ebola virus disease (EVD) in Liberia began in March 2014 and ended in January 2016. Epidemiological information on the EVD cases was collected and managed nationally; however, collection and management of the data were challenging at the time because surveillance and reporting systems malfunctioned during the outbreak. EVD diagnostic laboratories, however, were able to register basic demographic and clinical information of patients more systematically. Here we present data on 16,370 laboratory samples that were tested between April 4, 2014 and March 29, 2015. A total of 10,536 traceable individuals were identified, of whom 3,897 were confirmed cases (positive for Ebola virus RNA). There were significant differences in sex, age, and place of residence between confirmed and suspected cases that tested negative for Ebola virus RNA. Age (young children and the elderly) and place of residence (rural areas) were the risk factors for death due to the disease. The case fatality rate of confirmed cases decreased from 80% to 63% during the study period. These findings may help support future investigations and lead to a fuller understanding of the outbreak in Liberia.

Temperature modulates dengue virus epidemic growth rates through its effects on reproduction numbers and generation intervals.

Epidemic growth rate, r, provides a more complete description of the potential for epidemics than the more commonly studied basic reproduction number, R0, yet the former has never been described as a function of temperature for dengue virus or other pathogens with temperature-sensitive transmission. The need to understand the drivers of epidemics of these pathogens is acute, with arthropod-borne virus epidemics becoming increasingly problematic. We addressed this need by developing temperature-dependent descriptions of the two components of r-R0 and the generation interval-to obtain a temperature-dependent description of r. Our results show that the generation interval is highly sensitive to temperature, decreasing twofold between 25 and 35°C and suggesting that dengue virus epidemics may accelerate as temperatures increase, not only because of more infections per generation but also because of faster generations. Under the empirical temperature relationships that we considered, we found that r peaked at a temperature threshold that was robust to uncertainty in model parameters that do not depend on temperature. Although the precise value of this temperature threshold could be refined following future studies of empirical temperature relationships, the framework we present for identifying such temperature thresholds offers a new way to classify regions in which dengue virus epidemic intensity could either increase or decrease under future climate change.

From one to the other: responding to Ebola cases on either side of the line.

This case study is adapted from events that occurred along the Sierra Leone and Guinea land border during the 2014-2016 Ebola epidemic in West Africa. The response activities involved Sierra Leone and Guinea officials, along with assistance from U.S. Centers for Disease Control and Prevention (CDC) and the World Health Organisation (WHO). This case study builds upon an understanding of basic surveillance systems and outbreak response activities. Through this exercise, students will understand how to incorporate communication and coordination into surveillance and response efforts with counterparts across the border in neighbouring countries. This integration is important to reduce the spread of communicable diseases between neighbouring countries. The time required to complete this case study is 2-3 hours.

Contact tracing following outbreak of Ebola virus disease in urban settings in Nigeria.

An outbreak of Ebola virus disease occurred in Nigeria between July and September 2014. Contact tracing commenced in Lagos, and extended to Port Harcourt and Enugu as the outbreak continued to spread. A total of 899 contacts were traced. Contact tracing enhanced immediate identification of symptomatic contacts, some of whom eventually became cases. Contact tracing could be challenging in urban cities. However, use of electronic technology, adequate logistics, and highly skilled personnel enhanced the tracing of contacts to facilitate the successful containment of the outbreak. Nigeria was certified to be Ebola free on 21st October 2014. Ebola virus surveillance needs to be maintained to ensure the disease has been contained and to prevent future outbreaks. This case study aims to help trainees to review concepts, apply skills, and address challenges for contact tracing based on the experience of the Nigerian Field Epidemiology Training Network during the 2014 Ebola virus disease outbreak.

Response to an unusual outbreak in a high-risk situation.

In 2010, a series of lead poisoning outbreaks linked to artisanal gold processing killed at least 400 young children in Zamfara State in northwestern Nigeria. There were several efforts to respond to the outbreaks as they occurred. Subsequent recurrence of lead poisoning outbreaks within Zamfara and beyond suggested that there were no efforts to mitigate the outbreaks as recommended for disaster management. This case study, to be completed within 3 hours, is suitable for senior level public health officials and those training for such positions. It enables participants to review and apply epidemiological principles for managing disasters and suggest steps toward development of policy recommendations based on the context of environmental lead exposure. It will serve as a generic training module for managers/responders of other natural (floods, heat stroke) and man-made disasters (civil strife, conflict, insurgency) based on the general/standard principle of the complete disaster management cycle.

An epidemic of spastic paraparesis of unknown aetiology in Northern Mozambique.

This case study is based on a real-life outbreak investigation undertaken in Mozambique in 1981. This case study describes and promotes one particular approach to unknown disease outbreak investigation. Investigational procedures, however, may vary depending on location and outbreak. It is anticipated that the epidemiologist investigating an unknown disease outbreak will work within the framework of a "multidisciplinary investigation team". It is through the collaborative efforts of this team, with each member playing a critical role, that outbreak investigations are successfully completed. Some aspects of the original outbreak and investigation have, however, been altered to assist in meeting the desired teaching objectives and to allow completion of the case study in less than 3 hours.

Investigating an outbreak of measles in Margibi County, Liberia, October 2015.

The emergence and re-emergence of infectious diseases highlights the need to have well-trained field epidemiologists who will be at the forefront in the fight against these diseases, especially during an outbreak. Training for outbreak investigation is most effective when participants can develop their competencies in a practical exercise. To that end, this case study was based on a measles outbreak investigation conducted in Liberia during October 2015 by Liberia Frontline Field Epidemiology Training Program (FETP) residents, simulating steps to perform outbreak investigation in a real-life situation as a field epidemiologist. This case study is ideally suited to reinforce principles and skills already covered in a classroom lecture or in background reading by providing a practical training beyond the scope of theoretical learning. It is primarily intended for training novice public health practitioners who should be able to complete the exercises in approximately 3 hours.

Cholera outbreak in Homa Bay County, Kenya, 2015.

Cholera is among the re-emerging diseases in Kenya. Beginning in December 2014, a persistent outbreak occurred involving 29 out of the 47 countries. Homa Bay County in Western Kenya was among the first counties to report cholera cases from January to April 2015. This case study is based on an outbreak investigation conducted by FELTP residents in Homa Bay County in February 2015. It simulates an outbreak investigation including laboratory confirmation, active case finding, descriptive epidemiology and implementation of control measures. This case study is designed for the training of basic level field epidemiology trainees or any other health care workers working in public health-related fields. It can be administered in 2-3 hours. Used as adjunct training material, the case study provides the trainees with competencies in investigating an outbreak in preparation for the actual real-life experience of such outbreaks.

Unexplained haemorrhagic fever in Rural Ethiopia.

This case study was written based on events of an outbreak investigation of an unfamiliar disease in Ethiopia during October-December 2012. Ethiopia did not have reports of similar cases in the 50 years prior to this outbreak. In this case study, we recapitulate and analyse this outbreak investigation based on data gathered from the community, health facility, and laboratory systems. It can be used to teach: 1) the outbreak investigation process; 2) selection of appropriate epidemiological design for the investigation process, 3) basic statistical analysis of surveillance data, and 4) principals of disease control. The target audiences for this case study are officials working in public health and public health trainees. It will take at most 3.5 hours to complete this case study. At the end of the case study, participants should be able to apply the principals of outbreak investigation and use surveillance data to respond to an outbreak in their country-specific context.

Analysis of Dengue Serotype 4 in Sri Lanka during the 2012-2013 Dengue Epidemic.

The four serotypes of dengue virus (DENV-1, -2, -3, and -4) have had a rapidly expanding geographic range and are now endemic in over 100 tropical and subtropical countries. Sri Lanka has experienced periodic dengue outbreaks since the 1960s, but since 1989 epidemics have become progressively larger and associated with more severe disease. The dominant virus in the 2012 epidemic was DENV-1, but DENV-4 infections were also commonly observed. DENV-4 transmission was first documented in Sri Lanka when it was isolated from a traveler in 1978, but has been comparatively uncommon since dengue surveillance began in the early 1980s. To better understand the molecular epidemiology of DENV-4 infections in Sri Lanka, we conducted whole-genome sequencing on dengue patient samples from two different geographic locations. Phylogenetic analysis indicates that all sequenced DENV-4 strains belong to genotype 1 and are most closely related to DENV-4 viruses previously found in Sri Lanka and those recently found to be circulating in India and Pakistan.

Knowledge and Prevention Practices among U.S. Pregnant Immigrants from Zika Virus Outbreak Areas.

We administered an anonymous survey to assess knowledge, attitudes, and prevention practices related to the Zika virus among pregnant women residing in Texas. Multivariate logistic regression models controlling for age, race/ethnicity, education, and number of years in the United States assessed differences between women born in outbreak areas (N = 390) versus those born in the United States (N = 249). Results demonstrated that most women wanted more information on the Zika virus and desired to obtain it from their physician. The majority did not know that the Zika virus could be spread through sex with an asymptomatic partner or how often those infected were symptomatic. Few women took precautions to avoid mosquito bites. Only 40% reported frequently using repellent; 21% stated that cost was problematic and almost half were concerned about use during pregnancy. Three-fourths stated they would agree to vaccination, if available. Compared with U.S.-born women, those born in outbreak areas were more likely to have already discussed the Zika virus with their doctor (adjusted odds ratio [aOR] = 1.86, 95% confidence interval [CI] = 1.27, 2.71) and identify microcephaly as the most common birth defect (aOR = 2.59, 95% CI = 1.78, 3.76). Moreover, women born in outbreak areas were less likely to desire to keep it a secret if they became infected (aOR = 0.47, 95% CI = 0.31, 0.71). This study found that, regardless of birthplace, pregnant women need more education on the Zika virus disease and assurance regarding the safety of using repellent during pregnancy. They also need financial assistance for repellent, especially if living in states where transmission by mosquitos has been reported.

Measles Outbreak - Minnesota April-May 2017.

On April 10, 2017, the Minnesota Department of Health (MDH) was notified about a suspected measles case. The patient was a hospitalized child aged 25 months who was evaluated for fever and rash, with onset on April 8. The child had no history of receipt of measles-mumps-rubella (MMR) vaccine and no travel history or known exposure to measles. On April 11, MDH received a report of a second hospitalized, unvaccinated child, aged 34 months, with an acute febrile rash illness with onset on April 10. The second patient's sibling, aged 19 months, who had also not received MMR vaccine, had similar symptoms, with rash onset on March 30. Real-time reverse transcription-polymerase chain reaction (rRT-PCR) testing of nasopharyngeal swab or throat specimens performed at MDH confirmed measles in the first two patients on April 11, and in the third patient on April 13; subsequent genotyping identified genotype B3 virus in all three patients, who attended the same child care center. MDH instituted outbreak investigation and response activities in collaboration with local health departments, health care facilities, child care facilities, and schools in affected settings. Because the outbreak occurred in a community with low MMR vaccination coverage, measles spread rapidly, resulting in thousands of exposures in child care centers, schools, and health care facilities. By May 31, 2017, a total of 65 confirmed measles cases had been reported to MDH (Figure 1); transmission is ongoing.

Measles: Why it's still a threat.

A recent outbreak in Minnesota underscores the need to maintain vigilance and adhere to best practices in immunization and containment of known cases.

Enhanced Influenza Surveillance Using Telephone Triage and Electronic Syndromic Surveillance in the Department of Veterans Affairs, 2011-2015.

Telephone triage (TT) is a method whereby medical professionals speak by telephone to patients to assess their symptoms or health concerns and offer advice. These services are often administered through an electronic TT system, which guides TT professionals during the encounter through the use of structured protocols and algorithms to help determine the severity of the patients' health issue and refer them to appropriate care. TT is also an emerging data source for public health surveillance of infectious and noninfectious diseases, including influenza. We calculated Spearman correlation coefficients to compare the weekly number of US Department of Veterans Affairs (VA) TT calls with other conventional influenza measures for the 2011-2012 through 2014-2015 influenza seasons, for which there were a total of 35‚ÄČ666 influenza-coded TT encounters. Influenza-coded calls were strongly correlated with weekly VA influenza-coded hospitalizations (0.85), emergency department visits (0.90), influenza-like illness outpatient visits (0.92), influenza tests performed (0.86), positive influenza tests (0.82), and influenza antiviral prescriptions (0.89). The correlation between VA-TT and Centers for Disease Control and Prevention (CDC) national data for weekly influenza hospitalizations, influenza tests performed, and positive influenza tests was also strong. TT correlates well with VA health care use and CDC data and is a timely data source for monitoring influenza activity.

Harnessing Syndromic Surveillance Emergency Department Data to Monitor Health Impacts During the 2015 Special Olympics World Games.

Mass gatherings that attract a large international presence may cause or amplify point-source outbreaks of emerging infectious disease. The Los Angeles County Department of Public Health customized its syndromic surveillance system to detect increased syndrome-specific utilization of emergency departments (EDs) and other medical encounters coincident to the 2015 Special Olympics World Games.

Advancing the Use of Emergency Department Syndromic Surveillance Data, New York City, 2012-2016.

The use of syndromic surveillance has expanded from its initial purpose of bioterrorism detection. We present 6 use cases from New York City that demonstrate the value of syndromic surveillance for public health response and decision making across a broad range of health outcomes: synthetic cannabinoid drug use, heat-related illness, suspected meningococcal disease, medical needs after severe weather, asthma exacerbation after a building collapse, and Ebola-like illness in travelers returning from West Africa.

Outbreak characteristics associated with identification of contributing factors to foodborne illness outbreaks.

Information on the factors that cause or amplify foodborne illness outbreaks (contributing factors), such as ill workers or cross-contamination of food by workers, is critical to outbreak prevention. However, only about half of foodborne illness outbreaks reported to the United States' Centers for Disease Control and Prevention (CDC) have an identified contributing factor, and data on outbreak characteristics that promote contributing factor identification are limited. To address these gaps, we analyzed data from 297 single-setting outbreaks reported to CDC's new outbreak surveillance system, which collects data from the environmental health component of outbreak investigations (often called environmental assessments), to identify outbreak characteristics associated with contributing factor identification. These analyses showed that outbreak contributing factors were more often identified when an outbreak etiologic agent had been identified, when the outbreak establishment prepared all meals on location and served more than 150 meals a day, when investigators contacted the establishment to schedule the environmental assessment within a day of the establishment being linked with an outbreak, and when multiple establishment visits were made to complete the environmental assessment. These findings suggest that contributing factor identification is influenced by multiple outbreak characteristics, and that timely and comprehensive environmental assessments are important to contributing factor identification. They also highlight the need for strong environmental health and food safety programs that have the capacity to complete such environmental assessments during outbreak investigations.

Two Outbreaks of Trichinellosis Linked to Consumption of Walrus Meat - Alaska, 2016-2017.

During 1975-2012, CDC surveillance identified 1,680 trichinellosis cases in the United States with implicated food items; among these cases, 1,219 were attributed to consumption of raw or pork products, and 461 were attributed to nonpork products. Although trichinellosis in the United States has historically been associated with consumption of pork, multiple nonporcine species of wild game also are competent hosts for Trichinella spp. and have been collectively implicated in the majority of trichinellosis cases since the late 1990s (1-4) (Figure 1). During July 2016-May 2017, the Alaska Division of Public Health (ADPH) investigated two outbreaks of trichinellosis in the Norton Sound region associated with consumption of raw or undercooked walrus (Odobenus rosmarus) meat; five cases were identified in each of the two outbreaks. These were the first multiple-case outbreaks of walrus-associated trichinellosis in Alaska since 1992 (Figure 2). Health care providers should inquire about consumption of commercially prepared and personally harvested meats when evaluating suspected trichinellosis cases, especially in areas where consumption of wild game is commonplace.

On the origin and timing of Zika virus introduction in Brazil.

The timing and origin of Zika virus (ZIKV) introduction in Brazil has been the subject of controversy. Initially, it was assumed that the virus was introduced during the FIFA World Cup in June-July 2014. Then, it was speculated that ZIKV may have been introduced by athletes from French Polynesia (FP) who competed in a canoe race in Rio de Janeiro in August 2014. We attempted to apply mathematical models to determine the most likely time window of ZIKV introduction in Brazil. Given that the timing and origin of ZIKV introduction in Brazil may be a politically sensitive issue, its determination (or the provision of a plausible hypothesis) may help to prevent undeserved blame. We used a simple mathematical model to estimate the force of infection and the corresponding individual probability of being infected with ZIKV in FP. Taking into account the air travel volume from FP to Brazil between October 2013 and March 2014, we estimated the expected number of infected travellers arriving at Brazilian airports during that period. During the period between December 2013 and February 2014, 51 individuals travelled from FP airports to 11 Brazilian cities. Basing on the calculated force of ZIKV infection (the per capita rate of new infections per time unit) and risk of infection (probability of at least one new infection), we estimated that 18 (95% CI 12-22) individuals who arrived in seven of the evaluated cities were infected. When basic ZIKV reproduction numbers greater than one were assumed in the seven evaluated cities, ZIKV could have been introduced in any one of the cities. Based on the force of infection in FP, basic reproduction ZIKV number in selected Brazilian cities, and estimated travel volume, we concluded that ZIKV was most likely introduced and established in Brazil by infected travellers arriving from FP in the period between October 2013 and March 2014, which was prior to the two aforementioned sporting events.

Four years into the Indian ocean field epidemiology training programme.

Following the 2005-6 chikungunya outbreak, a project to strengthen regional Public Health preparedness in the Indian Ocean was implemented. It includes the Comoros, Madagascar, Mauritius, Reunion (France) and Seychelles. A Field Epidemiology Training Programme (FETP-OI) was started in 2011 to develop a pool of well-trained intervention epidemiologists.

A systematic review and meta-analysis on the incubation period of Campylobacteriosis.

Accurate knowledge of pathogen incubation period is essential to inform public health policies and implement interventions that contribute to the reduction of burden of disease. The incubation period distribution of campylobacteriosis is currently unknown with several sources reporting different times. Variation in the distribution could be expected due to host, transmission vehicle, and organism characteristics, however, the extent of this variation and influencing factors are unclear. The authors have undertaken a systematic review of published literature of outbreak studies with well-defined point source exposures and human experimental studies to estimate the distribution of incubation period and also identify and explain the variation in the distribution between studies. We tested for heterogeneity using I 2 and Kolmogorov-Smirnov tests, regressed incubation period against possible explanatory factors, and used hierarchical clustering analysis to define subgroups of studies without evidence of heterogeneity. The mean incubation period of subgroups ranged from 2·5 to 4·3 days. We observed variation in the distribution of incubation period between studies that was not due to chance. A significant association between the mean incubation period and age distribution was observed with outbreaks involving only children reporting an incubation of 1·29 days longer when compared with outbreaks involving other age groups.

Recognising clinical avian botulism in wild waterbirds.

This article has been prepared by Paul Duff and colleagues of the APHA Wildlife Expert Group.