International importation of measles virus--United States, 1993-2001

Air Passenger Travel and International Surveillance Data Predict Spatiotemporal Variation in Measles Importations to the United States

Measles incidence in the United States has grown dramatically, as vaccination rates are declining and transmission internationally is on the rise. Because imported cases are necessary drivers of outbreaks in non-endemic settings, predicting measles outbreaks in the US depends on predicting imported cases. To assess the predictability of imported measles cases, we performed a regression of imported measles cases in the US against an inflow variable that combines air travel data with international measles surveillance data. To understand the contribution of each data type to these predictions, we repeated the regression analysis with alternative versions of the inflow variable that replaced each data type with averaged values and with versions of the inflow variable that used modeled inputs. We assessed the performance of these regression models using correlation, coverage probability, and area under the curve statistics, including with resampling and cross-validation. Our regression model had good predictive ability with respect to the presence or absence of imported cases in a given state in a given year (area under the curve of the receiver operating characteristic curve (AUC) = 0.78) and the magnitude of imported cases (Pearson correlation = 0.84). By comparing alternative versions of the inflow variable averaging over different inputs, we found that both air travel data and international surveillance data contribute to the model's ability to predict numbers of imported cases and individually contribute to its ability to predict the presence or absence of imported cases. Predicted sources of imported measles cases varied considerably across years and US states, depending on which countries had high measles activity in a given year. Our results emphasize the importance of the relationship between global connectedness and the spread of measles. This study provides a framework for predicting and understanding imported case dynamics that could inform future studies and outbreak prevention efforts.

International Importations of Measles Virus into the United States During the Postelimination Era, 2001-2016

BACKGROUND

Although measles was declared eliminated from the United States in 2000, measles cases and outbreaks continue to occur, resulting from importations of the disease from countries where it remains endemic.

METHODS

We describe the epidemiology of international importations of measles virus into the United States during the postelimination era.

RESULTS

From 2001 to 2016, 553 imported measles cases were reported to the Centers for Disease Control and Prevention. A median of 28 importations occurred each year (range: 18-80). The median age of imported case-patients was 18 years (range: 3 months-75 years); 87% were unvaccinated or had an unknown vaccination status. US residents (as opposed to foreign visitors) accounted for 62% of imported measles cases. Overall, 62% of all imported case-patients reported travel to countries in the Western Pacific and European Regions of the World Health Organization during their exposure periods. The number of measles importations from specific countries was related to the incidence of measles in and the volume of travel to and from the source country.

CONCLUSIONS

Our findings emphasize the importance of measles vaccination of US residents aged ≥6 months before international travel according to the Advisory Committee on Immunization Practices recommendations and supporting global measles elimination efforts.

Occurrence of measles in a country with elimination status: Amplifying measles infection in hospitalized children due to imported virus

The Republic of Korea declared measles elimination in 2006. However, a measles outbreak occurred in 2013. This study aimed to identify the epidemiological characteristics of the sources of infection and the pattern of measles transmission in 2013 in South Korea. We utilized surveillance data, epidemiological data, immunization registry data, and genetic information. We describe the epidemiological characteristics of all measles case patients (sex, age distribution, vaccination status, sources of infection) as well as details of the outbreak (the pattern of transmission, duration, mean age of patients, and generation time). In 2013, a total of 107 measles cases were notified. Most patients were infants (43.0%) and unvaccinated individuals (60.7%). We identified 4 imported and 103 import-related cases. A total of 105 cases were related to four outbreaks that occurred in Gyeongnam, northern Gyeonggi, southern Gyeonggi, and Seoul. The predominant circulating genotype was B3 type, which was identified in the Gyeongnam, northern Gyeonggi, and southern Gyeonggi outbreaks. The B3 type had not been in circulation in South Korea in the previous 3 years; virologic evidence suggests that these outbreaks were import-related. Most measles cases in South Korea have been associated with imported measles virus. Although Korea has maintained a high level of herd immunity, clustering of susceptible people can cause such measles outbreaks.

Global Transmission Dynamics of Measles in the Measles Elimination Era

Although there have been many epidemiological reports of the inter-country transmission of measles, systematic analysis of the global transmission dynamics of the measles virus (MV) is limited. In this study, we applied phylogeographic analysis to characterize the global transmission dynamics of the MV using large-scale genetic sequence data (obtained for 7456 sequences) from 115 countries between 1954 and 2015. These analyses reveal the spatial and temporal characteristics of global transmission of the virus, especially in Australia, China, India, Japan, the UK, and the USA in the period since 1990. The transmission is frequently observed, not only within the same region but also among distant and frequently visited areas. Frequencies of export from measles-endemic countries, such as China, India, and Japan are high but decreasing, while the frequencies from countries where measles is no longer endemic, such as Australia, the UK, and the USA, are low but slightly increasing. The world is heading toward measles eradication, but the disease is still transmitted regionally and globally. Our analysis reveals that countries wherein measles is endemic and those having eliminated the disease (apart from occasional outbreaks) both remain a source of global transmission in this measles elimination era. It is therefore crucial to maintain vigilance in efforts to monitor and eradicate measles globally.

A review of factors affecting vaccine preventable disease in Japan

Japan is well known as a country with a strong health record. However its incidence rates of vaccine preventable diseases (VPD) such as hepatitis B, measles, mumps, rubella, and varicella remain higher than other developed countries. This article reviews the factors that contribute to the high rates of VPD in Japan. These include historical and political factors that delayed the introduction of several important vaccines until recently. Access has also been affected by vaccines being divided into government-funded "routine" (eg, polio, pertussis) and self-pay "voluntary" groups (eg, hepatitis A and B). Routine vaccines have higher rates of administration than voluntary vaccines. Administration factors include differences in well child care schedules, the approach to simultaneous vaccination, vaccination contraindication due to fever, and vaccination spacing. Parental factors include low intention to fully vaccinate their children and misperceptions about side effects and efficacy. There are also provider knowledge gaps regarding indications, adverse effects, interval, and simultaneous vaccination. These multifactorial issues combine to produce lower population immunization rates and a higher incidence of VPD than other developed countries. This article will provide insight into the current situation of Japanese vaccinations, the issues to be addressed and suggestions for public health promotion.

Molecular epidemiology of measles virus in Italy, 2002-2007

Background

The European Regional Office of the World Health Organization (WHO/Europe) developed a strategic approach to halt the indigenous transmission of measles in its 53 Member States by 2015. In view of the goal of measles elimination, it is of great importance to assess the circulation of wild-type measles virus (MV). Genetic analysis is indispensable to understand the epidemiology of measles.

Methods

Urine and saliva samples were collected between May 2002 and December 2007, in order to find the origins and routes of wild type measles virus circulation. RT-PCR was performed on a total of 414 clinical samples of patients from different Italian regions. The results confirmed the genome presence in 199 samples, out of which 179 were sequenced. The sequences were genotyped by comparing the fragment coding for the carboxyl terminus of the nucleoprotein (450 nucleotides) with that one of the WHO reference strains.

Results

From the year 2002 to the year 2007 phylogenetic analysis of measles sequences showed a predominant circulation of the D7 genotype in the Italian territory for the years 2002–2004. This genotype was replaced by D4 and B3 genotypes in the biennium 2006–2007. During the same period C2, A, D5 and D8 genotypes were also detected.

Conclusions

Genetic characterization of wild-type MV provides a means to study the transmission pathways of the virus, and is an essential component of laboratory-based surveillance. Knowledge of currently circulating measles virus genotype in Italy will help in monitoring the success of the measles elimination programme and will contribute to evaluate the effectiveness of future vaccination campaigns.

Vaccine preventable diseases in returned international travelers: results from the GeoSentinel Surveillance Network

Vaccine preventable diseases (VPDs) threaten international travelers, but little is known about their epidemiology in this group. We analyzed records of 37,542 ill returned travelers entered into the GeoSentinel Surveillance Network database. Among 580 (1.5%) with VPDs, common diagnoses included enteric fever (n=276), acute viral hepatitis (n=148), and influenza (n=70). Factors associated with S. typhi included VFR travel (p<0.016) to South Central Asia (p<0.001). Business travel was associated with influenza (p<0.001), and longer travel with hepatitis A virus (p=0.02). 29% of those with VPDs had pre-travel consultations. At least 55% of those with VPDs were managed as inpatients, compared to 9.5% of those with non-VPDs. Three deaths occurred; one each due to pneumococcal meningitis, S. typhi, and rabies. VPDs are significant contributors to morbidity and potential mortality in travelers. High rates of hospitalization make them an attractive target for pre-travel intervention.

Vaccination coverage against measles in German-born and foreign-born children and identification of unvaccinated subgroups in Germany

Data from the representative German Health Interview and Examination Survey for Children and Adolescents were used to identify unvaccinated subgroups that should be targeted by vaccination programmes in order to interrupt measles transmission. Measles vaccination coverage was low among children below the age of 3, having > or =3 siblings and in foreign-born migrants. Multivariate analyses show that vaccination coverage was strongly related to the place of birth in migrants: foreign-born children have a three-fold odds of being unvaccinated. Odds were also higher in children living in former West Germany, having > or =3 siblings, and it was especially high in children with parents reporting reservations against vaccinations.

Further efforts needed to achieve measles elimination in Germany: results of an outbreak investigation

OBJECTIVE

To determine morbidity and costs related to a large measles outbreak in Germany and to identify ways to improve the country's national measles elimination strategy.

METHODS

We investigated a large outbreak of measles in the federal state of North Rhine-Westphalia (NRW) that occurred in 2006 after 2 years of low measles incidence (< 1 case per 100,000). WHO's clinical case definition was used, and surveillance data from 2006 and 2001 were compared. All cases notified in Duisburg, the most severely affected city, were contacted and interviewed or sent a questionnaire. Health-care provider costs were calculated using information on complications, hospitalization and physician consultations.

FINDINGS

In NRW, 1749 cases were notified over a 48-week period. Compared with 2001, the distribution of cases shifted to older age groups (especially the 10-14 year group). Most cases (n = 614) occurred in Duisburg. Of these, 81% were interviewed; 15% were hospitalized and two died. Of the 464 for whom information was available, 80% were reported as unvaccinated. Common reasons for non-vaccination were parents either forgetting (36%) or rejecting (28%) vaccination. The average cost per measles case was estimated at 373 euros.

CONCLUSION

An accumulation of non-immune individuals led to this outbreak. The shift in age distribution has implications for the effectiveness of measles control and the elimination strategy in place. Immediate nationwide school-based catch-up vaccination campaigns targeting older age groups are needed to close critical immunity gaps. Otherwise, the elimination of measles in Germany and thus in Europe by 2010 will not be feasible.

Measles exportation from Japan to the United States, 1994 to 2006

BACKGROUND

Imported measles cases and outbreaks involving Japanese travelers have been reported from the United States and other countries. For the United States, Japan is the top country of origin. The aims of this study were to analyze measles exportation trends from Japan to the United States and to suggest recommendations for improving monitoring and control in both countries.

METHODS

Reviewing all exportation cases reported to the Centers for Disease Control and Prevention and sentinel measles activity data monitored by the Japanese Ministry of Health between January 1994 and December 2006 (observation period).

RESULTS

A total of 63 cases were reported (median = 4 cases per year). Cases ranged in age from 9 months to 53 years (median = 17 y). Peaks occurred at 13 to 26 years and 12 to 35 months. Six cases were US citizens and 57 Japanese. Ten cases were reported in July and August, followed by eight in February and March. Twenty-seven cases were reported from Hawaii, followed by 15 from California and 6 from New York. Seven cases developed the secondary spread. Three of the cases had previously received one dose of measles vaccine, compared to 35 who were never immunized (25 cases unknown). During the observation period, measles activity exceeded the warning level in 157 weeks, with measles exportation occurring the subsequent week for 30 of these weeks. In comparison, during the 521 weeks in which measles activity was below the warning level, exportation of measles the following week was observed for 21 of those weeks (OR = 5.62, 95% CI = 3.12-10.2, p < 0.001).

CONCLUSIONS

Trend of exported measles cases from Japan to the United States has corresponded with the measles activity trend in Japan. Most of the cases were unvaccinated. This international health problem should be solved by strong leadership of Japanese public health professionals.

Implications of a 2005 measles outbreak in Indiana for sustained elimination of measles in the United States

BACKGROUND

Measles was declared eliminated from the United States in 2000 but remains endemic worldwide. In 2005, a 17-year-old unvaccinated girl who was incubating measles returned from Romania, creating the largest documented outbreak of measles in the United States since 1996.

METHODS

We conducted a case-series investigation, molecular typing of viral isolates, surveys of rates of vaccination coverage, interviews regarding attitudes toward vaccination, and cost surveys.

RESULTS

Approximately 500 persons attended a gathering with the index patient one day after her return home. Approximately 50 lacked evidence of measles immunity, of whom 16 (32 percent) acquired measles at the gathering. During the six weeks after the gathering, a total of 34 cases of measles were confirmed. Of the patients with confirmed measles, 94 percent were unvaccinated, 88 percent were less than 20 years of age, and 9 percent were hospitalized. Of the 28 patients who were 5 to 19 years of age, 71 percent were home-schooled. Vaccine failure occurred in two persons. The virus strain was genotype D4, which is endemic in Romania. Although containment measures began after 20 persons were already infectious, measles remained confined mostly to children whose parents had refused to have them vaccinated, primarily out of concern for adverse events from the vaccine. Seventy-one percent of patients were from four households. Levels of measles-vaccination coverage in Indiana were 92 percent for preschoolers and 98 percent for sixth graders. Estimated costs of containing the disease were at least 167,685 dollars, including 113,647 dollars at a hospital with an infected employee.

CONCLUSIONS

This outbreak was caused by the importation of measles into a population of children whose parents had refused to have them vaccinated because of safety concerns about the vaccine. High vaccination levels in the surrounding community and low rates of vaccine failure averted an epidemic. Maintenance of high rates of vaccination coverage, including improved strategies of communication with persons who refuse vaccination, is necessary to prevent future outbreaks and sustain the elimination of measles in the United States.

Measles outbreak in the Republic of the Marshall Islands, 2003

BACKGROUND

Measles is a highly contagious viral infection. Measles transmission can be prevented through high population immunity (>or=95%) achieved by measles vaccination. In the Republic of the Marshall Islands (RMI), no measles cases were reported during 1989-2002; however, a large measles outbreak occurred in 2003. Reported 1-dose measles vaccine coverage among children aged 12-23 months varied widely (52-94%) between 1990 and 2000.

METHODS

RMI is a Pacific island nation (1999 population: 50,840). A measles case was defined as fever, rash, and cough, or coryza, or conjunctivitis, in an RMI resident between July 13 and November 7, 2003. A vaccination campaign was used for outbreak control.

RESULTS

Of the 826 reported measles cases, 766 (92%) occurred in the capital (Majuro). There were 186 (23%) cases in infants aged <1 year and 309 (37%) of cases in persons aged >or=15 years. The attack rate was highest among infants (Majuro atoll: 213 cases/1,000 infants). Among cases aged 1-14 years, 281 (59%) reported no measles vaccination before July 2003. There were 100 hospitalizations and 3 deaths. The measles H1 genotype was identified. The vaccination campaign resulted in 93% coverage among persons aged 6 months to 40 years. Interpretation Populations without endemic measles transmission can accumulate substantial susceptibility and be at risk for large outbreaks when measles virus is imported. 'Islands' of measles susceptibility may develop in infants, adults, and any groups with low vaccine coverage. To prevent outbreaks, high population immunity must be sustained by maintaining and documenting high vaccine coverage.

Measles

PURPOSE OF REVIEW

The purpose of this review is to summarize important papers concerning measles disease and measles-containing vaccines published in 2004.

RECENT FINDINGS

Endemic measles has been successfully controlled in the Americas and, to a lesser extent, in Europe. This has been achieved with a high uptake of two doses of a measles-containing vaccine. Even in industrialized countries, where vaccine uptake is poor, for example Japan, the disease is still a significant cause of morbidity and mortality. Vaccine failure is predominantly due to primary vaccine failure, which may, in part, be genetic in origin and related to HLA type. Measles-containing vaccines have been shown to be associated with febrile convulsions, but there is no strong evidence of a link with atopy. There is considerable evidence that there is no causal relationship with autistic disorders. In spite of this, many parents and some professionals have concerns about the safety of the vaccines, which may lead to their underuse.

SUMMARY

It is possible to eliminate measles with a high uptake of two doses of measles-containing vaccine, but concerns about safety persist and need to be tackled. More research is required into how to do this effectively and also to elucidate the causes of vaccine failure.

Emerging infectious disease issues in international adoptions: severe acute respiratory syndrome (SARS), avian influenza and measles

PURPOSE OF REVIEW

New emerging infections over the last few years demonstrate the potential for the introduction of epidemic illness through global migration. The increasing number of children adopted internationally (>20,000 in 2003, from the United States State Department) provides a unique situation for the spread of emerging infections through the combination of international travel by parents through areas where such infections may be contracted and the nature of the living conditions for many of the orphans being placed by this process.

RECENT FINDINGS

The recent literature on three emerging infections--avian influenza, severe acute respiratory syndrome (SARS) and measles--describes clinical aspects of the illnesses and their epidemiology. For avian influenza aspects of the agrarian economy in southeast Asia enabled the virus to reach the human population. The potential for further adaptation to people could set the stage for a new pandemic. SARS evolved in rural China and spread worldwide in one season with an approximate 10% mortality. Attention to public-health measures led to control of this new illness. Most recently, outbreaks of measles in Chinese orphanages have been documented. These findings demonstrate the potential of such infections to be transmitted during the process of international adoption, and in the case of measles the realization of this potential in recent reported cases from Chinese orphanages brought to the United States on commercial airlines.

SUMMARY

Clinicians involved in international adoption and public-health officials assessing emerging infections need to work together in monitoring these issues.

Defining and assessing measles elimination goals

Although 3 of 6 World Health Organization regions have established measles elimination targets, measles elimination goals are not well defined. In general, disease elimination has been defined as the reduction of incidence in a population to zero. However, measles is so contagious that zero incidence is difficult to achieve and sustain because the risk of imported measles remains while measles is endemic in any country. Also, imported cases will occasionally result in short chains of indigenous transmission unless a country achieves 100% immunity. Therefore, the United States currently uses the absence of endemic measles (i.e., no indigenous chains of transmission persisting for >or=1 year) as the programmatic goal for measles elimination. To document the absence of endemic measles in the United States, we compiled information on the epidemiology of measles, genotype distribution, population immunity, and adequacy of measles surveillance. A panel of experts, convened in March 2000 to review the data, concluded that measles is no longer endemic in the United States.

Has Surveillance Been Adequate to Detect Endemic Measles in the United States?

Evidence that endemic measles has been eliminated in the United States rests on the performance of the surveillance system. Information from national surveillance data allows us to evaluate the adequacy of national surveillance to detect the circulation of endemic measles. Sources of data include measles report dates, international importation status, and the size of chains of measles transmission. The proportion of chains of measles transmission that can be epidemiologically linked to international importations is high (62%), as would be expected if measles is no longer circulating; the number of imported cases, although lower than estimated expected values, is within a reasonable range of expectation. National surveillance detects even small outbreaks, so larger outbreaks that are the marker for endemic transmission would almost certainly be detected. Few unreported cases of measles are detected when health departments conduct careful investigations in response to reports of an index case. Surveillance appears to be adequate to support the contention that measles is no longer endemic in the United States.

Lessons Learned from Establishing and Evaluating Indicators of the Quality of Measles Surveillance in the United States, 1996–1998

As part of a strategy to eliminate measles, 7 indicators were adopted in the United States in 1996 to ensure the quality of measles surveillance. This report summarizes the US experience with these indicators during 1996-1998. The indicators are compiled from data reported to the Centers for Disease Control and Prevention (CDC) during routine surveillance supplemented with information collected directly from states. Measles case investigations are generally thorough, and sufficient information is collected to control and monitor disease. A high proportion of measles cases are imported from other countries, suggesting that investigations are complete. For some states, the lag from disease onset to reporting is long, and the number of health department investigations of measleslike illnesses is low. Most of these investigations include laboratory testing of clinical specimens. Collection of measles virus specimens from cases for genetic analysis needs improvement. The CDC and health departments need to continue efforts directed at health care professionals to ensure the recognition, proper diagnostic workup, and reporting of measles.