Early Detection of Severe Acute Respiratory Syndrome Coronavirus 2 Variants Using Traveler-based Genomic Surveillance at 4 US Airports, September 2021-January 2022.

We enrolled arriving international air travelers in a severe acute respiratory syndrome coronavirus 2 genomic surveillance program. We used molecular testing of pooled nasal swabs and sequenced positive samples for sublineage. Traveler-based surveillance provided early-warning variant detection, reporting the first US Omicron BA.2 and BA.3 in North America.

Effect of Predeparture Testing on Postarrival SARS-CoV-2-Positive Test Results Among International Travelers - CDC Traveler-Based Genomic Surveillance Program, Four U.S. Airports, March-September 2022.

Beginning December 6, 2021, all international air passengers boarding flights to the United States were required to show either a negative result from a SARS-CoV-2 viral test taken ≤1 day before departure or proof of recovery from COVID-19 within the preceding 90 days (1). As of June 12, 2022, predeparture testing was no longer mandatory but remained recommended by CDC (2,3). Various modeling studies have estimated that predeparture testing the day before or the day of air travel reduces transmission or importation of SARS-CoV-2 by 31%-76% (4-7). Postarrival SARS-CoV-2 pooled testing data from CDC's Traveler-based Genomic Surveillance program were used to compare SARS-CoV-2 test results among volunteer travelers arriving at four U.S. airports during two 12-week periods: March 20-June 11, 2022, when predeparture testing was required, and June 12-September 3, 2022, when predeparture testing was not required. In a multivariable logistic regression model, pooled nasal swab specimens collected during March 20-June 11 were 52% less likely to be positive for SARS-CoV-2 than were those collected during June 12-September 3, after adjusting for COVID-19 incidence in the flight's country of origin, sample pool size, and collection airport (adjusted odds ratio [aOR] = 0.48, 95% CI = 0.39-0.58) (p<0.001). These findings support predeparture testing as a tool for reducing travel-associated SARS-CoV-2 transmission and provide important real-world evidence that can guide decisions for future outbreaks and pandemics.

Cruise Ship Travel in the Era of Coronavirus Disease 2019 (COVID-19): A Summary of Outbreaks and a Model of Public Health Interventions.

BACKGROUND: Cruise travel contributed to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission when there were relatively few cases in the United States. By 14 March 2020, the Centers for Disease Control and Prevention (CDC) issued a No Sail Order suspending US cruise operations; the last US passenger ship docked on 16 April. METHODS: We analyzed SARS-CoV-2 outbreaks on cruises in US waters or carrying US citizens and used regression models to compare voyage characteristics. We used compartmental models to simulate the potential impact of 4 interventions (screening for coronavirus disease 2019 (COVID-19) symptoms; viral testing on 2 days and isolation of positive persons; reduction of passengers by 40%, crew by 20%, and reducing port visits to 1) for 7-day and 14-day voyages. RESULTS: During 19 January to 16 April 2020, 89 voyages on 70 ships had known SARS-CoV-2 outbreaks; 16 ships had recurrent outbreaks. There were 1669 reverse transcription polymerase chain reaction (RT-PCR)-confirmed SARS-CoV-2 infections and 29 confirmed deaths. Longer voyages were associated with more cases (adjusted incidence rate ratio, 1.10, 95% confidence interval [CI]: 1.03-1.17, P < .003). Mathematical models showed that 7-day voyages had about 70% fewer cases than 14-day voyages. On 7-day voyages, the most effective interventions were reducing the number of individuals onboard (43.3% reduction in total infections) and testing passengers and crew (42% reduction in total infections). All four interventions reduced transmission by 80.1%, but no single intervention or combination eliminated transmission. Results were similar for 14-day voyages. CONCLUSIONS: SARS-CoV-2 outbreaks on cruises were common during January-April 2020. Despite all interventions modeled, cruise travel still poses a significant SARS-CoV-2 transmission risk.

Coronavirus Disease 2019 (COVID-19) in Americans Aboard the Diamond Princess Cruise Ship.

BACKGROUND: The Diamond Princess cruise ship was the site of a large outbreak of coronavirus disease 2019 (COVID-19). Of 437 Americans and their travel companions on the ship, 114 (26%) tested positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). METHODS: We interviewed 229 American passengers and crew after disembarkation following a ship-based quarantine to identify risk factors for infection and characterize transmission onboard the ship. RESULTS: The attack rate for passengers in single-person cabins or without infected cabinmates was 18% (58/329), compared with 63% (27/43) for those sharing a cabin with an asymptomatic infected cabinmate, and 81% (25/31) for those with a symptomatic infected cabinmate. Whole genome sequences from specimens from passengers who shared cabins clustered together. Of 66 SARS-CoV-2-positive American travelers with complete symptom information, 14 (21%) were asymptomatic while on the ship. Among SARS-CoV-2-positive Americans, 10 (9%) required intensive care, of whom 7 were ≥70 years. CONCLUSIONS: Our findings highlight the high risk of SARS-CoV-2 transmission on cruise ships. High rates of SARS-CoV-2 positivity in cabinmates of individuals with asymptomatic infections suggest that triage by symptom status in shared quarters is insufficient to halt transmission. A high rate of intensive care unit admission among older individuals complicates the prospect of future cruise travel during the pandemic, given typical cruise passenger demographics. The magnitude and severe outcomes of this outbreak were major factors contributing to the Centers for Disease Control and Prevention's decision to halt cruise ship travel in US waters in March 2020.

Reducing travel-related SARS-CoV-2 transmission with layered mitigation measures: symptom monitoring, quarantine, and testing.

BACKGROUND: Balancing the control of SARS-CoV-2 transmission with the resumption of travel is a global priority. Current recommendations include mitigation measures before, during, and after travel. Pre- and post-travel strategies including symptom monitoring, antigen or nucleic acid amplification testing, and quarantine can be combined in multiple ways considering different trade-offs in feasibility, adherence, effectiveness, cost, and adverse consequences. METHODS: We used a mathematical model to analyze the expected effectiveness of symptom monitoring, testing, and quarantine under different estimates of the infectious period, test-positivity relative to time of infection, and test sensitivity to reduce the risk of transmission from infected travelers during and after travel. RESULTS: If infection occurs 0-7 days prior to travel, immediate isolation following symptom onset prior to or during travel reduces risk of transmission while traveling by 30-35%. Pre-departure testing can further reduce risk, with testing closer to the time of travel being optimal even if test sensitivity is lower than an earlier test. For example, testing on the day of departure can reduce risk while traveling by 44-72%. For transmission risk after travel with infection time up to 7 days prior to arrival at the destination, isolation based on symptom monitoring reduced introduction risk at the destination by 42-56%. A 14-day quarantine after arrival, without symptom monitoring or testing, can reduce post-travel risk by 96-100% on its own. However, a shorter quarantine of 7 days combined with symptom monitoring and a test on day 5-6 after arrival is also effective (97--100%) at reducing introduction risk and is less burdensome, which may improve adherence. CONCLUSIONS: Quarantine is an effective measure to reduce SARS-CoV-2 transmission risk from travelers and can be enhanced by the addition of symptom monitoring and testing. Optimal test timing depends on the effectiveness of quarantine: with low adherence or no quarantine, optimal test timing is close to the time of arrival; with effective quarantine, testing a few days later optimizes sensitivity to detect those infected immediately before or while traveling. These measures can complement recommendations such as social distancing, using masks, and hand hygiene, to further reduce risk during and after travel.

Risk Assessment and Management of COVID-19 Among Travelers Arriving at Designated U.S. Airports, January 17-September 13, 2020.

In January 2020, with support from the U.S. Department of Homeland Security (DHS), CDC instituted an enhanced entry risk assessment and management (screening) program for air passengers arriving from certain countries with widespread, sustained transmission of SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19). The objectives of the screening program were to reduce the importation of COVID-19 cases into the United States and slow subsequent spread within states. Screening aimed to identify travelers with COVID-19-like illness or who had a known exposure to a person with COVID-19 and separate them from others. Screening also aimed to inform all screened travelers about self-monitoring and other recommendations to prevent disease spread and obtain their contact information to share with public health authorities in destination states. CDC delegated postarrival management of crew members to airline occupational health programs by issuing joint guidance with the Federal Aviation Administration.* During January 17-September 13, 2020, a total of 766,044 travelers were screened, 298 (0.04%) of whom met criteria for public health assessment; 35 (0.005%) were tested for SARS-CoV-2, and nine (0.001%) had a positive test result. CDC shared contact information with states for approximately 68% of screened travelers because of data collection challenges and some states' opting out of receiving data. The low case detection rate of this resource-intensive program highlighted the need for fundamental change in the U.S. border health strategy. Because SARS-CoV-2 infection and transmission can occur in the absence of symptoms and because the symptoms of COVID-19 are nonspecific, symptom-based screening programs are ineffective for case detection. Since the screening program ended on September 14, 2020, efforts to reduce COVID-19 importation have focused on enhancing communications with travelers to promote recommended preventive measures, reinforcing mechanisms to refer overtly ill travelers to CDC, and enhancing public health response capacity at ports of entry. More efficient collection of contact information for international air passengers before arrival and real-time transfer of data to U.S. health departments would facilitate timely postarrival public health management, including contact tracing, when indicated. Incorporating health attestations, predeparture and postarrival testing, and a period of limited movement after higher-risk travel, might reduce risk for transmission during travel and translocation of SARS-CoV-2 between geographic areas and help guide more individualized postarrival recommendations.

Travel-Associated Zika Virus Disease Acquired in the Americas Through February 2016: A GeoSentinel Analysis.

Background: Zika virus has spread rapidly in the Americas and has been imported into many nonendemic countries by travelers. Objective: To describe clinical manifestations and epidemiology of Zika virus disease in travelers exposed in the Americas. Design: Descriptive, using GeoSentinel records. Setting: 63 travel and tropical medicine clinics in 30 countries. Patients: Ill returned travelers with a confirmed, probable, or clinically suspected diagnosis of Zika virus disease seen between January 2013 and 29 February 2016. Measurements: Frequencies of demographic, trip, and clinical characteristics and complications. Results: Starting in May 2015, 93 cases of Zika virus disease were reported. Common symptoms included exanthema (88%), fever (76%), and arthralgia (72%). Fifty-nine percent of patients were exposed in South America; 71% were diagnosed in Europe. Case status was established most commonly by polymerase chain reaction (PCR) testing of blood and less often by PCR testing of other body fluids or serology and plaque-reduction neutralization testing. Two patients developed Guillain-Barré syndrome, and 3 of 4 pregnancies had adverse outcomes (microcephaly, major fetal neurologic abnormalities, and intrauterine fetal death). Limitation: Surveillance data collected by specialized clinics may not be representative of all ill returned travelers, and denominator data are unavailable. Conclusion: These surveillance data help characterize the clinical manifestations and adverse outcomes of Zika virus disease among travelers infected in the Americas and show a need for global standardization of diagnostic testing. The serious fetal complications observed in this study highlight the importance of travel advisories and prevention measures for pregnant women and their partners. Travelers are sentinels for global Zika virus circulation and may facilitate further transmission. Primary Funding Source: Centers for Disease Control and Prevention, International Society of Travel Medicine, and Public Health Agency of Canada.

Addressing a Yellow Fever Vaccine Shortage - United States, 2016-2017.

Recent manufacturing problems resulted in a shortage of the only U.S.-licensed yellow fever vaccine. This shortage is expected to lead to a complete depletion of yellow fever vaccine available for the immunization of U.S. travelers by mid-2017. CDC, the Food and Drug Administration (FDA), and Sanofi Pasteur are collaborating to ensure a continuous yellow fever vaccine supply in the United States. As part of this collaboration, Sanofi Pasteur submitted an expanded access investigational new drug (eIND) application to FDA in September 2016 to allow for the importation and use of an alternative yellow fever vaccine manufactured by Sanofi Pasteur France, with safety and efficacy comparable to the U.S.-licensed vaccine; the eIND was accepted by FDA in October 2016. The implementation of this eIND protocol included developing a systematic process for selecting a limited number of clinic sites to provide the vaccine. CDC and Sanofi Pasteur will continue to communicate with the public and other stakeholders, and CDC will provide a list of locations that will be administering the replacement vaccine at a later date.

Estimation of Severe Middle East Respiratory Syndrome Cases in the Middle East, 2012-2016.

Using data from travelers to 4 countries in the Middle East, we estimated 3,250 (95% CI 1,300-6,600) severe cases of Middle East respiratory syndrome occurred in this region during September 2012-January 2016. This number is 2.3-fold higher than the number of laboratory-confirmed cases recorded in these countries.

Assessment of the potential for international dissemination of Ebola virus via commercial air travel during the 2014 west African outbreak.

BACKGROUND: The WHO declared the 2014 west African Ebola epidemic a public health emergency of international concern in view of its potential for further international spread. Decision makers worldwide are in need of empirical data to inform and implement emergency response measures. Our aim was to assess the potential for Ebola virus to spread across international borders via commercial air travel and assess the relative efficiency of exit versus entry screening of travellers at commercial airports. METHODS: We analysed International Air Transport Association data for worldwide flight schedules between Sept 1, 2014, and Dec 31, 2014, and historic traveller flight itinerary data from 2013 to describe expected global population movements via commercial air travel out of Guinea, Liberia, and Sierra Leone. Coupled with Ebola virus surveillance data, we modelled the expected number of internationally exported Ebola virus infections, the potential effect of air travel restrictions, and the efficiency of airport-based traveller screening at international ports of entry and exit. We deemed individuals initiating travel from any domestic or international airport within these three countries to have possible exposure to Ebola virus. We deemed all other travellers to have no significant risk of exposure to Ebola virus. FINDINGS: Based on epidemic conditions and international flight restrictions to and from Guinea, Liberia, and Sierra Leone as of Sept 1, 2014 (reductions in passenger seats by 51% for Liberia, 66% for Guinea, and 85% for Sierra Leone), our model projects 2.8 travellers infected with Ebola virus departing the above three countries via commercial flights, on average, every month. 91,547 (64%) of all air travellers departing Guinea, Liberia, and Sierra Leone had expected destinations in low-income and lower-middle-income countries. Screening international travellers departing three airports would enable health assessments of all travellers at highest risk of exposure to Ebola virus infection. INTERPRETATION: Decision makers must carefully balance the potential harms from travel restrictions imposed on countries that have Ebola virus activity against any potential reductions in risk from Ebola virus importations. Exit screening of travellers at airports in Guinea, Liberia, and Sierra Leone would be the most efficient frontier at which to assess the health status of travellers at risk of Ebola virus exposure, however, this intervention might require international support to implement effectively. FUNDING: Canadian Institutes of Health Research.

Projected Zika Virus Importation and Subsequent Ongoing Transmission after Travel to the 2016 Olympic and Paralympic Games - Country-Specific Assessment, July 2016.

Zika virus belongs to the genus Flavivirus of the family Flaviviridae; it is transmitted to humans primarily through the bite of an infected Aedes species mosquito (e.g., Ae. aegypti and Ae. albopictus) (1). Zika virus has been identified as a cause of congenital microcephaly and other serious brain defects (2). As of June 30, 2016, CDC had issued travel notices for 49 countries and U.S. territories across much of the Western hemisphere (3), including Brazil, where the 2016 Olympic and Paralympic Games (Games of the XXXI Olympiad, also known as Rio 2016; Games) will be hosted in Rio de Janeiro in August and September 2016. During the Games, mosquito-borne Zika virus transmission is expected to be low because August and September are winter months in Brazil, when cooler and drier weather typically reduces mosquito populations (4). CDC conducted a risk assessment to predict those countries susceptible to ongoing Zika virus transmission resulting from introduction by a single traveler to the Games. Whereas all countries are at risk for travel-associated importation of Zika virus, CDC estimated that 19 countries currently not reporting Zika outbreaks have the environmental conditions and population susceptibility to sustain mosquito-borne transmission of Zika virus if a case were imported from infection at the Games. For 15 of these 19 countries, travel to Rio de Janeiro during the Games is not estimated to increase substantially the level of risk above that incurred by the usual aviation travel baseline for these countries. The remaining four countries, Chad, Djibouti, Eritrea, and Yemen, are unique in that they do not have a substantial number of travelers to any country with local Zika virus transmission, except for anticipated travel to the Games. These four countries will be represented by a projected, combined total of 19 athletes (plus a projected delegation of about 60 persons), a tiny fraction of the 350,000-500,000 visitors expected at the Games.* Overall travel volume to the Games represents a very small fraction (<0.25%) of the total estimated 2015 travel volume to Zika-affected countries,(†) highlighting the unlikely scenario that Zika importation would be solely attributable to travel to the Games. To prevent Zika virus infection and its complications among athletes and visitors to the Games and importation of Zika virus into countries that could sustain local transmission, pregnant women should not travel to the Games, mosquito bites should be avoided while traveling and for 3 weeks after returning home, and measures should be taken to prevent sexual transmission (Box).

Notes from the Field: Splenomegaly of Unknown Etiology in Congolese Refugees Applying for Resettlement to the United States - Uganda, 2015.

Approximately 70,000-90,000 refugees are resettled to the United States each year, and during the next 5 years, 50,000 Congolese refugees are expected to arrive in the United States. The International Organization for Migration (IOM) performs refugee medical examinations overseas for the U.S. Refugee Resettlement Program. In 2014, IOM reported that a large number of U.S.-bound Congolese refugees from Uganda had spleens that were enlarged on examination. During two evaluations of refugee populations in western Uganda in March and July 2015, refugees with splenomegaly on physical examination were offered additional assessment and treatment, including abdominal ultrasonography and laboratory testing. Among 987 persons screened, 145 (14.7%) had splenomegaly and received further testing. Among the 145 patients with splenomegaly, 63.4% were aged 5-17 years (median = 14.8 years). There was some evidence of family clustering, with 33 (22.7%) of the 145 cases occurring in families.

Effect of a culture-based screening algorithm on tuberculosis incidence in immigrants and refugees bound for the United States: a population-based cross-sectional study.

BACKGROUND: Before 2007, immigrants and refugees bound for the United States were screened for tuberculosis (TB) by a smear-based algorithm that could not diagnose smear-negative/culture-positive TB. In 2007, the Centers for Disease Control and Prevention implemented a culture-based algorithm. OBJECTIVE: To evaluate the effect of the culture-based algorithm on preventing the importation of TB to the United States by immigrants and refugees from foreign countries. DESIGN: Population-based, cross-sectional study. SETTING: Panel physician sites for overseas medical examination. PATIENTS: Immigrants and refugees with TB. MEASUREMENTS: Comparison of the increase of smear-negative/culture-positive TB cases diagnosed overseas among immigrants and refugees by the culture-based algorithm with the decline of reported cases among foreign-born persons within 1 year after arrival in the United States from 2007 to 2012. RESULTS: Of the 3 212 421 arrivals of immigrants and refugees from 2007 to 2012, a total of 1 650 961 (51.4%) were screened by the smear-based algorithm and 1 561 460 (48.6%) were screened by the culture-based algorithm. Among the 4032 TB cases diagnosed by the culture-based algorithm, 2195 (54.4%) were smear-negative/culture-positive. Before implementation (2002 to 2006), the annual number of reported cases among foreign-born persons within 1 year after arrival was relatively constant (range, 1424 to 1626 cases; mean, 1504 cases) but decreased from 1511 to 940 cases during implementation (2007 to 2012). During the same period, the annual number of smear-negative/culture-positive TB cases diagnosed overseas among immigrants and refugees bound for the United States by the culture-based algorithm increased from 4 to 629. LIMITATION: This analysis did not control for the decline in new arrivals of nonimmigrant visitors to the United States and the decrease of incidence of TB in their countries of origin. CONCLUSION: Implementation of the culture-based algorithm may have substantially reduced the incidence of TB among newly arrived, foreign-born persons in the United States. PRIMARY FUNDING SOURCE: None.

A Tale of Many Cities: A Contemporary Historical Study of the Implementation of School Closures during the 2009 pA(H1N1) Influenza Pandemic.

Applying qualitative historical methods, we examined the consideration and implementation of school closures as a nonpharmaceutical intervention (NPI) in thirty US cities during the spring 2009 wave of the pA(H1N1) influenza pandemic. We gathered and performed close textual readings of official federal, state, and municipal government documents; media coverage; and academic publications. Lastly, we conducted oral history interviews with public health and education officials in our selected cities. We found that several local health departments pursued school closure plans independent of CDC guidance, that uncertainty of action and the rapidly evolving understanding of pA(H1N1) contributed to tension and pushback from the public, that the media and public perception played a significant role in the response to school closure decisions, and that there were some notable instances of interdepartmental communication breakdown. We conclude that health departments should continue to develop and fine-tune their action plans while also working to develop better communication methods with the public, and work more closely with education officials to better understand the complexities involved in closing schools. Lastly, state and local governments should work to resolve lingering issues of legal authority for school closures in times of public health crises.

Albendazole therapy and enteric parasites in United States-bound refugees.

BACKGROUND: Beginning on May 1, 1999, the Centers for Disease Control and Prevention (CDC) recommended presumptive treatment of refugees for intestinal parasites with a single dose of albendazole (600 mg), administered overseas before departure for the United States. METHODS: We conducted a retrospective cohort study involving 26,956 African and Southeast Asian refugees who were screened by means of microscopical examination of stool specimens for intestinal parasites on resettlement in Minnesota between 1993 and 2007. Adjusted prevalence ratios for intestinal nematodes, schistosoma species, giardia, and entamoeba were calculated among refugees who migrated before versus those who migrated after the CDC recommendation of presumptive predeparture albendazole treatment. RESULTS: Among 4370 untreated refugees, 20.8% had at least one stool nematode, most commonly hookworm (in 9.2%). Among 22,586 albendazole-treated refugees, only 4.7% had one or more nematodes, most commonly trichuris (in 3.9%). After adjustment for sex, age, and region, albendazole-treated refugees were less likely than untreated refugees to have any nematodes (prevalence ratio, 0.19), ascaris (prevalence ratio, 0.06), hookworm (prevalence ratio, 0.07), or trichuris (prevalence ratio, 0.27) but were not less likely to have giardia or entamoeba. Schistosoma ova were identified exclusively among African refugees and were less prevalent among those treated with albendazole (prevalence ratio, 0.60). After implementation of the albendazole protocol, the most common pathogens among 17,011 African refugees were giardia (in 5.7%), trichuris (in 5.0%), and schistosoma (in 1.8%); among 5575 Southeast Asian refugees, only giardia remained highly prevalent (present in 17.2%). No serious adverse events associated with albendazole use were reported. CONCLUSIONS: Presumptive albendazole therapy administered overseas before departure for the United States was associated with a decrease in the prevalence of intestinal nematodes among newly arrived African and Southeast Asian refugees.

A cost-benefit analysis of a proposed overseas refugee latent tuberculosis infection screening and treatment program.

BACKGROUND: This study explored the effect of screening and treatment of refugees for latent tuberculosis infection (LTBI) before entrance to the United States as a strategy for reducing active tuberculosis (TB). The purpose of this study was to estimate the costs and benefits of LTBI screening and treatment in United States bound refugees prior to arrival. METHODS: Costs were included for foreign and domestic LTBI screening and treatment and the domestic treatment of active TB. A decision tree with multiple Markov nodes was developed to determine the total costs and number of active TB cases that occurred in refugee populations that tested 55, 35, and 20 % tuberculin skin test positive under two models: no overseas LTBI screening and overseas LTBI screening and treatment. For this analysis, refugees that tested 55, 35, and 20 % tuberculin skin test positive were divided into high, moderate, and low LTBI prevalence categories to denote their prevalence of LTBI relative to other refugee populations. RESULTS: For a hypothetical 1-year cohort of 100,000 refugees arriving in the United States from regions with high, moderate, and low LTBI prevalence, implementation of overseas screening would be expected to prevent 440, 220, and 57 active TB cases in the United States during the first 20 years after arrival. The cost savings associated with treatment of these averted cases would offset the cost of LTBI screening and treatment for refugees from countries with high (net cost-saving: $4.9 million) and moderate (net cost-saving: $1.6 million) LTBI prevalence. For low LTBI prevalence populations, LTBI screening and treatment exceed expected future TB treatment cost savings (net cost of $780,000). CONCLUSIONS: Implementing LTBI screening and treatment for United States bound refugees from countries with high or moderate LTBI prevalence would potentially save millions of dollars and contribute to United States TB elimination goals. These estimates are conservative since secondary transmission from tuberculosis cases in the United States was not considered in the model.

Implementation of new TB screening requirements for U.S.-bound immigrants and refugees - 2007-2014.

For more than two decades, as the number of tuberculosis (TB) cases overall in the United States has declined, the proportion of cases among foreign-born persons has increased. In 2013, the percentage of TB cases among those born outside the country was 64.6%. To address this trend, CDC has developed strategies to identify and treat TB in U.S.-bound immigrants and refugees overseas. Each year, approximately 450,000 persons are admitted to the United States on an immigrant visa, and 50,000-70,000 are admitted as refugees. Applicants for either an immigrant visa or refugee status are required to undergo a medical examination overseas before being allowed to travel to the United States. CDC is the federal agency with regulatory oversight of the overseas medical examination, and panel physicians appointed by the U.S. Department of State perform the examinations in accordance with Technical Instructions (TI) provided by CDC's Division of Global Migration and Quarantine (DGMQ). Beginning in 1991, the algorithm for TB TI relied on chest radiographs for applicants aged ≥15 years, followed by sputum smears for those with findings suggestive of TB; no additional diagnostics were used. In 2007, CDC issued enhanced standards for TB diagnosis and treatment, including the addition of sputum cultures (which are more sensitive than smears) as a diagnostic tool and treatment delivered as directly observed therapy (DOT). This report summarizes worldwide implementation of the new screening requirements since 2007. In 2012, the year for which the most recent data are available, 60% of the TB cases diagnosed were in persons with smear-negative, but culture-positive, test results. The results demonstrate that rigorous diagnostic and treatment programs can be implemented in areas with high TB incidence overseas.

Effectiveness of a school district closure for pandemic influenza A (H1N1) on acute respiratory illnesses in the community: a natural experiment.

BACKGROUND: Following detection of pandemic influenza A H1N1 (pH1N1) in Dallas/Fort Worth, Texas, a school district (intervention community, [IC]) closed all public schools for 8 days to reduce transmission. Nearby school districts (control community [CC]) mostly remained open. METHODS: We collected household data to measure self-reported acute respiratory illness (ARI), before, during, and after school closures. We also collected influenza-related visits to emergency departments (ED(flu)). RESULTS: In both communities, self-reported ARIs and ED(flu) visits increased from before to during the school closure, but the increase in ARI rates was 45% lower in the IC (0.6% before to 1.2% during) than in the CC (0.4% before to 1.5% during) (RRR(During)(/Before) = 0.55, P < .001; adjusted OR(During/Before) = 0.49, P < .03). For households with school-aged children only (no children 0-5 years), IC had even lower increases in adjusted ARI than in the CC (adjusted OR(During/Before) = 0.28, P < .001). The relative increase of total ED(flu) visits in the IC was 27% lower (2.8% before to 4.4% during) compared with the CC (2.9% before to 6.2% during). Among children aged 6-18 years, the percentage of ED(flu) in IC remained constant (5.1% before vs 5.2% during), whereas in the CC it more than doubled (5.2% before vs 10.9% during). After schools reopened, ARI rates and ED(flu) visits decreased in both communities. CONCLUSIONS: Our study documents a reduction in ARI and ED(flu) visits in the intervention community. Our findings can be used to assess the potential benefit of school closures during pandemics.

Entry and exit screening of airline travellers during the A(H1N1) 2009 pandemic: a retrospective evaluation.

OBJECTIVE: To evaluate the screening measures that would have been required to assess all travellers at risk of transporting A(H1N1)pdm09 out of Mexico by air at the start of the 2009 pandemic. METHODS: Data from flight itineraries for travellers who flew from Mexico were used to estimate the number of international airports where health screening measures would have been needed, and the number of travellers who would have had to be screened, to assess all air travellers who could have transported the H1N1 influenza virus out of Mexico during the initial stages of the 2009 A(H1N1) pandemic. FINDINGS: Exit screening at 36 airports in Mexico, or entry screening of travellers arriving on direct flights from Mexico at 82 airports in 26 other countries, would have resulted in the assessment of all air travellers at risk of transporting A(H1N1)pdm09 out of Mexico at the start of the pandemic. Entry screening of 116 travellers arriving from Mexico by direct or connecting flights would have been necessary for every one traveller at risk of transporting A(H1N1)pdm09. Screening at just eight airports would have resulted in the assessment of 90% of all air travellers at risk of transporting A(H1N1)pdm09 out of Mexico in the early stages of the pandemic. CONCLUSION: During the earliest stages of the A(H1N1) pandemic, most public health benefits potentially attainable through the screening of air travellers could have been achieved by screening travellers at only eight airports.