International Course in Applied Epidemiology FREE

MMWR. 2001;50:148

CDC and Emory University's Rollins School of Public Health will co-sponsor a course, "International Course in Applied Epidemiology," during September 24–October 19, 2001, in Atlanta, Georgia. This basic course in epidemiology is directed at public health professionals from countries other than the United States.

The course's content includes presentations and discussions of epidemiologic principles, basic statistical analysis, public health surveillance, field investigations, surveys and sampling, and discussions of the epidemiologic aspects of current major public health problems in international health. Included are small group discussions of epidemiologic case exercises based on field investigations. Participants are encouraged to give a short presentation reviewing some epidemiologic data from their own country. Computer training using Epi Info 2000 (Windows® version), a software program developed at CDC and the World Health Organization for epidemiologists, is included. Prerequisites are familiarity with the vocabulary and principles of basic epidemiology or completion of CDC's "Principles of Epidemiology" homestudy course (SS3030) or equivalent. Preference will be given to applicants whose work involves priority public health problems in inter-national health. Early registration deadline is June 1, 2001; late registration deadline is September 1, 2001. There is a tuition charge.

Additional information and applications are available from Emory University, Rollins School of Public Health, International Health Dept.(PIA), 1518 Clifton Road N.E., Room 746, Atlanta, GA 30322; telephone (404) 7273485; fax (404) 7274590; World-Wide Web site, http://www.sph.emory.edu/EPICOURSES*; or e-mail pvaleri@sph.emory.edu.

*References to sites of nonCDC organizations on the WorldWide Web are provided as a service to MMWR readers and do not constitute or imply endorsement of these organizations or their programs by CDC or the U.S. Department of Health and Human Services. CDC is not responsible for the content of pages found at these sites.

MMWR. 2001;50:140-143

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Mercury (Hg), a heavy metal, is widespread and persistent in the environment. Exposure to hazardous Hg levels can cause permanent neurologic and kidney impairment.^1- 3 Elemental or inorganic Hg released into the air or water becomes methylated in the environment where it accumulates in animal tissues and increases in concentration through the food chain. The U.S. population primarily is exposed to methylmercury by eating fish. Methylmercury exposures to women of childbearing age are of great concern because a fetus is highly susceptible to adverse effects. This report presents preliminary estimates of blood and hair Hg levels from the 1999 National Health and Nutrition Examination Survey (NHANES 1999) and compares them with a recent toxicologic review by the National Research Council (NRC). The findings suggest that Hg levels in young children and women of childbearing age generally are below those considered hazardous. These preliminary estimates show that approximately 10% of women have Hg levels within one tenth of potentially hazardous levels indicating a narrow margin of safety for some women and supporting efforts to reduce methylmercury exposure.

CDC's NHANES is a continuous survey of the health and nutritional status of the U.S. civilian, noninstitutionalized population with each year of data constituting a representative population sample. A household interview and a physical examination were conducted for each survey participant. During the physical examination, blood was collected by venipuncture for all persons aged ≥1 year and hair samples, consisting of approximately 100 strands, were cut from the occipital position of the head of children aged 1-5 years and women aged 16-49 years. Whole blood specimens were analyzed for total Hg and inorganic Hg for children aged 1-5 years and women aged 16-49 years by automated cold vapor atomic absorption spectrophotometry in CDC's trace elements laboratory. The detection limit was 0.2 parts per billion (ppb) for total Hg and 0.4 ppb for inorganic Hg.⁴ Hairs of 0.6 inches (1.5 cm) closest to the scalp (approximately 1 month's growth) were analyzed for total Hg concentration using cold vapor atomic fluorescence spectroscopy.⁵ The limit of detection for total Hg in hair varied by analytic batch; the maximum limit of detection (0.1 parts per million [ppm]) was used in these analyses. Blood Hg levels less than the limit of detection were assigned a value equal to the detection limit divided by the square root of two for calculation of geometric mean values.

The geometric mean total blood Hg concentration for all women aged 16-49 years and children aged 1-5 years was 1.2 ppb and 0.3 ppb, respectively; the 90th percentile of blood Hg for women and children was 6.2 ppb and 1.4 ppb, respectively. Almost all inorganic Hg levels were undetectable; therefore, these measures indicate blood methylmercury levels. The 90th percentile of hair Hg for women and children was 1.4 ppm and 0.4 ppm, respectively. Geometric mean values were not calculated for hair Hg values.

Center for Food Safety and Applied Nutrition, Food and Drug Administration. US Environmental Protection Agency. National Energy Technology Laboratory, Dept of Energy. National Marine Fisheries Laboratory, National Oceanic and Atmospheric Administration. National Center for Health Statistics; National Center for Environmental Health, CDC.

The NHANES 1999 blood and hair Hg data are the first nationally representative human tissue measures of the U.S. population's exposure to Hg. Previous estimates of methylmercury exposure in the general population were based on exposure models using fish tissue Hg concentrations and dietary recall survey data.¹ The NRC review provided guidance to the Environmental Protection Agency (EPA) for developing an exposure reference dose for methylmercury (i.e., an estimated daily exposure that probably is free of risk for adverse effects over the course of a person's life).³ The NRC report recommended statistical modeling of results from an epidemiologic study conducted in the Faroe Islands near Iceland, where methylmercury exposures are high because of the large amount of seafood eaten by the local population. Results of this study were used to calculate a benchmark dose (BMD), an estimate of a methylmercury exposure in utero associated with an increase in the prevalence of abnormal scores on cognitive function tests in children. The lower 95% confidence limit of the BMD (BMDL*) was recommended to calculate the EPA reference dose. The NRC committee recommended a BMDL of 58 ppb Hg in cord blood (corresponding to 12 ppm Hg in maternal hair).³ In the NHANES 1999 sample, there were no measurements of blood values ≥58 ppb or hair values ≥12 ppm. A margin-of-exposure analysis (i.e., an evaluation of the ratio of BMDL to estimated population exposure levels) showed ratios of <10 when comparing BMDL with NHANES 1999 estimates of the 90th percentile for blood and hair Hg levels in women of childbearing age. Margin-of-exposure measures of this magnitude indicate a narrow margin of safety³ and suggest that efforts aimed at decreasing human exposure to methylmercury should continue.

The findings in this study are subject to at least three limitations. First, the ratio of Hg in cord and maternal blood is uncertain. The NRC committee summarized some studies that suggest that cord blood values may be 20%-30% higher than corresponding maternal blood levels. However, other studies suggest that the ratio is closer to 1:1³; therefore, the NHANES values may not be directly comparable to BMDL recommended by NRC. Second, NHANES cannot provide estimates of Hg exposure in certain highly exposed groups (e.g., subsistence fishermen and others who eat large amounts of fish). Published data from studies of highly exposed U.S. populations indicated that some persons attain Hg tissue levels above BMDL.¹ Third, the sample size of NHANES 1999 was small and the 1999 survey was conducted in only 12 locations. More data are needed to confirm these findings.

The long-term strategy for reducing exposure to Hg is to lower concentrations of Hg in fish by limiting Hg releases into the atmosphere from burning mercury-containing fuel and waste and from other industrial processes. On the basis of data from EPA's National Toxics Inventory, air emissions of Hg decreased approximately 21% during 1990-1996, largely because of regulations for waste incineration.⁷ EPA expects this trend to continue as regulations are implemented for waste incineration and chlorine production facilities and are developed for electric power utilities.^8- 9 Fish is high in protein and nutrients and low in saturated fatty acids and cholesterol and should be considered an important part of the diet. The short-term strategy to reduce Hg exposure is to eat fish with low Hg levels and to avoid or to moderate intake of fish with high Hg levels. State-based fish advisories and bans identify fish species contaminated by Hg and their locations and provide safety advice (http://www.epa.gov/ost/fish†). The Food and Drug Administration advises that pregnant women and those who may become pregnant should not eat shark, swordfish, king mackerel, and tile fish known to contain elevated levels of methylmercury. Information is available at http://www.fda.gov/bbs/topics/ANSWERS/2001/advisory.html.†

U.S. population estimates of Hg tissue levels by race/ethnicity, region, and fish consumption will become available after 2 additional years of NHANES data collection. NHANES will provide the opportunity to measure tissue Hg levels and to monitor the effectiveness of continuing efforts to reduce methylmercury exposure in the U.S. population.

*A BMD of 85 ppb Hg in cord blood or 17 ppm Hg in maternal hair was estimated to result in an increase in the proportion of abnormal scores on the Boston Naming Test for children exposed in utero from an estimated background prevalence of 5% to a prevalence of 10%.⁶ BMDL recommended by NRC is the lower 95% confidence bound of the BMD.

†References to sites of nonCDC organizations on the World-Wide Web are provided as a service to MMWR readers and do not constitute or imply endorsement of these organizations or their programs by CDC or the U.S. Department of Health and Human Services. CDC is not responsible for the content of pages found at these sites.

MMWR. 2001;50:97-98

Every year approximately two million pilgrims from more than 140 countries gather in Saudi Arabia for a pilgrimage to the holy places of Islam known as the Hajj. Coinciding with the Hajj pilgrimage during March 2000, Saudi Arabian health officials identified an outbreak of meningococcal disease; a substantial proportion of the isolates were the bacterial strain Neisseria meningitidis serogroup W-135. Four cases of meningococcal disease subsequently were identified among the estimated 15,000 pilgrims returning to the United States, their close contacts, and community. In addition, approximately 400 cases of meningococcal disease caused by N. meningitidis serogroup W-135 were identified worldwide during 2000.¹ Whether an outbreak of meningococcal disease will recur in 2001 is unknown.

Following an outbreak of serogroup A meningococcal disease associated with the Hajj during 1987, the Saudi Arabian government required all pilgrims to receive the meningococcal polysaccharide vaccine.² In the United States, the available vaccine, quadrivalent meningococcal polysaccharide vaccine, contains serogroup W-135 polysaccharide. However, vaccination does not protect against asymptomatic nasopharyngeal carriage of the bacteria. Persons may transmit N. meningitidis infection to close contacts upon their return from Saudi Arabia, and taking an antibiotic can reduce the risk for transmission and disease. It is not known whether returning pilgrims will have increased rates of acquisition of nasopharyngeal carriage of N. meningitidis.

To assess the risk for meningococcal disease in returning pilgrims and their close contacts, CDC is planning to evaluate nasopharyngeal carriage among a set of pilgrims returning from the Hajj. The results of this evaluation and any recommendations will be posted on the World-Wide Web, http://www.cdc.gov/travel, when they become available. Information also will be available by telephone, (888) 232-3228.

MMWR. 2001;50:147-148

During July 12, 2000–February 8, 2001, 12 laboratory-confirmed poliomyelitis cases attributed to vaccine-derived poliovirus type 1 were identified in the Dominican Republic.¹ Of these, 11 (92%) case-patients were aged ≤6 years (range: 9 months–14 years), and the date of paralysis onset of the last case was January 2, 2001. All case-patients were inadequately vaccinated or unvaccinated. In Haiti, one confirmed polio case attributed to vaccine-derived type 1 poliovirus was reported in an unvaccinated child aged 2 years with paralysis onset on August 30, 2000. As of February 21, 33 acute flaccid paralysis (AFP) cases from the Dominican Republic and three AFP cases from Haiti were pending final classification.

Extensive control efforts are under way. The Dominican Republic held nationwide mass vaccination campaigns with oral poliovirus vaccine (OPV) in December 2000 and February 2001, with a third round planned for April 2001. All children aged <5 years are being targeted, with approximately 1.2 million OPV doses given in the first campaign. AFP surveillance has been strengthened with intensification of active case-finding and weekly reporting. Haiti has initiated regional OPV campaigns to be conducted approximately every 2 months.

Travelers to the Dominican Republic and Haiti who are not vaccinated adequately are at risk for polio. All travelers should be vaccinated against polio according to national vaccination policies.*²

Ministry of Health, Pan American Health Organization, Santo Domingo, Dominican Republic. Ministry of Health, Pan American Health Organization, Port-au-Prince, Haiti. Caribbean Epidemiology Center Laboratory, Pan American Health Organization, Trinidad and Tobago. Div of Vaccines and Immunization, Pan American Health Organization, Washington, DC. Respiratory and Enteric Viruses Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Vaccine Preventable Disease Eradication Div, National Immunization Program, CDC.

*Recommendations for children in the United States include a 4-dose vaccination series with inactivated poliovirus vaccine (IPV) at ages 2, 4, 6-18 months, and 4-6 years. Unvaccinated adults should receive three doses of IPV, the first two doses at intervals of 4-8 weeks and the third dose 6-12 months after the second. If three doses cannot be administered within the recommended intervals before protection is needed, alternative schedules are proposed. For incompletely vaccinated persons, additional IPV doses are recommended to complete a series. Booster doses of IPV may be considered for persons who previously have completed a primary series of polio vaccination and who may be traveling to areas where polio is endemic.