Estimating Annual Births to Hepatitis B Surface Antigen–Positive Women in the United States by Using Data on Maternal Country of Birth

Abstract

Objective:

A national estimate of births to hepatitis B surface antigen (HBsAg)–positive women can help public health programs plan surveillance, educational, and outreach activities to improve identification and management of at-risk women and infants. Stratifying mothers by country of birth allows for the application of region-specific HBsAg prevalence estimates, which can more precisely estimate the number of at-risk infants. The objective of our study was to estimate the number of births to HBsAg-positive women in the United States with more granularity than previous models.

Methods:

We developed a model that incorporated maternal country of birth (MCOB) and updated HBsAg prevalence estimates. We assessed birth certificate data by MCOB, and we stratified US-born mothers by race/ethnicity, US territory–born mothers by territory, and non–US-born mothers by region. We multiplied and summed data in each subcategory by using HBsAg prevalence estimates calculated from the 2009-2014 National Health and Nutrition Examination Surveys or Perinatal Hepatitis B Prevention Program. We compared the findings of our MCOB model with a race/ethnicity model.

Results:

In 2015, an estimated 20 678 infants were born to HBsAg-positive women in the United States, representing 0.5% of all births. Births to US-born and non–US-born women comprised 77.2% and 21.5% of all births, respectively, and 40.1% and 57.9% of estimated births to HBsAg-positive women, respectively. The estimated contribution of births to HBsAg-positive women varied by MCOB region, from 4 (0.03%) infants born to women from Australia/Oceania to 5795 (28.0%) infants born to women from East Asia. Our MCOB model estimated 5666 fewer births to HBsAg-positive women than did the race/ethnicity model.

Conclusions:

As global vaccine programs reduce HBsAg prevalence, the MCOB model can incorporate evolving HBsAg prevalence estimates for women from various regions of the world.

Globally, approximately 257 million persons are chronically infected with hepatitis B virus (HBV).¹ In the United States, an estimated 850 000 to 2 million persons have chronic HBV infection.^2,3 Mother-to-child transmission of HBV infection contributes disproportionately to new infections in infants.⁴ In the United States, the Advisory Committee on Immunization Practices recommends (1) routine screening of all pregnant women for hepatitis B surface antigen (HBsAg) to identify active HBV infection and (2) initiation of postexposure prophylaxis consisting of monovalent hepatitis B vaccine and hepatitis B immune globulin within 12 hours of birth for infants born to HBsAg-positive women.^5,6 Infant postexposure prophylaxis followed by a complete hepatitis B vaccine series (≥3 doses total) is up to 95% effective in preventing mother-to-child transmission of HBV infection.^5,7 Among HBV-infected infants, 90% develop chronic hepatitis B,^8-10 which confers a 25% lifetime risk of premature death from complications such as liver failure and liver cancer and perpetuates the cycle of mother-to-child transmission.⁵

Identifying HBsAg-positive pregnant women is a crucial first step toward ensuring that infants receive timely postexposure prophylaxis to prevent mother-to-child transmission. Since 1990, Perinatal Hepatitis B Prevention Programs (PHBPPs) funded by the Centers for Disease Control and Prevention (CDC) have been tasked with identifying HBsAg-positive pregnant women and case-managing their infants. CDC models estimate the expected number of annual births to HBsAg-positive pregnant women.^11,12 PHBPPs use these estimates to set goals for identifying HBsAg-positive women and their infants toward prevention of mother-to-child transmission of hepatitis B.

To estimate the number of expected births to HBsAg-positive women, CDC uses a multiplier model (race/ethnicity model) in which total annual births are multiplied by race- and ethnicity-specific HBsAg prevalence among women. The race/ethnicity model obtains these HBsAg prevalence estimates from the National Health and Nutrition Examination Survey (NHANES) with the exception of Asian/Pacific Islander women, for whom estimates were obtained from the medical literature because of small sample size.^12,13 Data on Asian/Pacific Islander women were also assessed by US-born and non–US-born status because data on HBsAg prevalence among Asian/Pacific Islander women differ by place of birth.^12,13 Programmatic data indicate that fewer than half of estimated infants born to HBsAg-positive women were identified by PHBPPs since 1994.¹²

Immigration to the United States from HBV endemic areas (ie, areas with HBsAg prevalence ≥2%) increased after 1950,^11,14,15 leading to an increase in non–US-born persons with potential chronic HBV infection living in the United States.² To address these population changes and to more closely estimate births to HBsAg-positive women, in 2011, Din et al¹⁶ added maternal country of birth (MCOB) to the existing CDC race/ethnicity model. However, their model was limited to 22 US states that provided data on MCOB on a high percentage of birth certificates.¹⁶

During 2003-2015, a substantial number of states adopted the revised 2003 US Standard Certificate of Live Birth, which includes collection of MCOB; by 2015, 48 states and the District of Columbia had adopted the revised birth certificate form.¹⁷ Hepatitis B vaccination among US adolescents has increased; studies demonstrate that vaccination increased from 81.3% in 2006¹⁸ to 91.9% in 2017.¹⁹ Beginning in the 1990s, comprehensive infant and childhood hepatitis B vaccination campaigns were initiated in many HBV endemic countries.²⁰ These changes are expected to decrease the prevalence of HBsAg-positive US-born and non–US-born women of childbearing age in the United States. Therefore, a model accounting for contemporary HBsAg prevalence is needed. To better estimate the number of births to HBsAg-positive women in the United States, we developed a revised model—the MCOB model—that incorporates MCOB and race/ethnicity and uses updated HBsAg prevalence estimates.

Methods

Birth Certificate Data

Birth certificate data are submitted by 57 US vital statistics jurisdictions to CDC’s National Center for Health Statistics (unpublished data from 57 vital statistics jurisdictions, National Center for Health Statistics, 2010-2015). We analyzed data on live births in the United States (50 states and the District of Columbia) during 2010-2015 to US resident women (unpublished data from 57 vital statistics jurisdictions, National Center for Health Statistics, 2010-2015) and present results from 2015. Births to non-US residents account for approximately 0.2% of all US births, and we excluded these births from analysis because the current race/ethnicity model estimates also exclude non-US residents. All 50 states and the District of Columbia reported data on maternal race/ethnicity and MCOB to the National Center for Health Statistics during 2010-2015.

We stratified data on infants by MCOB: US-born mothers (50 states and the District of Columbia), US territory–born mothers, non–US-born mothers, and mothers whose country of birth was unknown. We categorized US territory–born mothers separately from non–US-born mothers because these territories have CDC-funded PHBPPs that affect infant hepatitis B vaccination practices. We substratified data on infants born to US-born mothers by maternal race/ethnicity (non-Hispanic white, non-Hispanic black, Hispanic, Asian/Pacific Islander, and other/unknown). We substratified data on infants born to US territory–born mothers by maternal territory of birth (American Samoa, Guam, Northern Mariana Islands, Puerto Rico, and US Virgin Islands). Using maternal birth countries from the National Center for Health Statistics database, we substratified data on non–US-born mothers into 16 geographic regions adapted from the previous literature: Africa, Australia/Oceania, East Asia, South Asia, Southeast Asia, West and Central Asia, Caribbean (except Haiti), Eastern Europe, Western and Northern Europe, Southern Europe, Haiti, Mexico and Central America, Middle East, North America, Pacific Islands, and South America.^16,21 Because of data limitations, we did not further stratify data on infants born to US territory–born women and non–US-born women by maternal race/ethnicity.

HBsAg Prevalence

We based HBsAg prevalence estimates on infant’s maternal race/ethnicity and/or country of birth. We derived data for these estimates from NHANES²² and PHBPP (unpublished data from national PHBPP, National Center for Immunization and Respiratory Diseases, 2007-2014)²³ (Table 1).

Table 1.

Categorization of infants by maternal country of birth and sources of corresponding HBsAg prevalence estimates, United States, 2009-2015

Maternal Country of Birtha	Source of Data on HBsAg Prevalence	HBsAg Prevalence Cohort
US-borna
Non-Hispanic white	2009-2014 NHANES22	Women of all ages and birth origins
Non-Hispanic black	2009-2014 NHANES22
Hispanic	2009-2014 NHANES22
Asian/Pacific Islander	2011-2014 NHANES22
Other/unknown	2009-2014 NHANES22
US territory-born
American Samoa	2009-2011 PHBPP annual reportsb	Live births to HBsAg-positive women in individual territory (proxy for HBsAg-positive pregnant women in each territory)
Guam	2009-2014 PHBPP annual reportsb
Northern Mariana Islands	2009-2014 PHBPP annual reportsb
Puerto Rico	2009-2014 PHBPP annual reportsb
US Virgin Islands	2009-2012 PHBPP annual reportsb
Non–US-born
Africa	Walker et al 2016 (Enhanced Perinatal Hepatitis B Case Management Projects)23	Live births to HBsAg-positive women in individual region (proxy for HBsAg-positive pregnant women in each region)
East Asia
South Asia
Southeast Asia
West/Central Asia
Australia
Caribbean (except Haiti)
Eastern Europe
Southern Europe
Western and Northern Europe
Haiti
Mexico and Central America
Middle East
North America
Pacific Islands
South America
Unknown
Not applicable	2009-2014 NHANES22	Women of all ages and birth origins

Abbreviations: HBsAg, hepatitis B surface antigen; NHANES, National Health and Nutrition Examination Survey; PHBPP, Perinatal Hepatitis B Prevention Program.

^aData on maternal country of birth, territory of birth, and race/ethnicity were sourced from National Center for Health Statistics birth certificate data (unpublished data from 57 vital statistics jurisdictions, National Center for Health Statistics, 2010-2015). Regions of birth for women born outside the United States were adapted from previous studies.^{16, 21}

^bPHBPP annual reports: Unpublished data from national Perinatal Hepatitis B Prevention Program, National Center for Immunization and Respiratory Diseases, 2007-2014.

US-Born Women

For infants born to US-born women, we determined a race/ethnicity–specific HBsAg prevalence from pooled 2009-2014 NHANES data, with the exception of Asian/Pacific Islanders, for whom data collection was limited to 2011-2014.²² We identified women as being infected with HBV if they had a positive HBsAg test result.

We conducted weighted analyses of NHANES data to calculate adjusted prevalence estimates of noninstitutionalized US women with HBsAg infection. We also calculated adjusted prevalence estimates for age group, race/ethnicity, and non–US-born status. We multiplied adjusted prevalence estimates expressed as percentages to population totals provided by the National Center for Health Statistics, averaged during 2009-2014, to express the resulting prevalence estimates as the equivalent number of persons residing in US households. To account for the effects of potential confounding among the selected characteristics, we used a multivariate logistic regression model to calculate the adjusted prevalence estimates. In the model, HBsAg status served as the dependent variable, and age group, race/ethnicity, and non–US-born status served as independent variables. For all groups, we used 95% confidence intervals (CIs) of adjusted HBsAg prevalence specific to each racial/ethnic category for lower and upper limits of estimated range of births. Because the NHANES sample size was limited, we used prevalence estimates among all women (regardless of age or non–US-born status) for the US-born category and applied these estimates to the MCOB model.

US Territory–Born Women

For infants born to US territory–born women, we approximated HBsAg prevalence estimates for American Samoa, Guam, Northern Mariana Islands, Puerto Rico, and US Virgin Islands from PHBPP data. Because limited data on HBsAg prevalence in these regions were available, we calculated a proxy for HBsAg prevalence among pregnant women as follows: we divided the annual number of births to HBsAg-positive women identified by PHBPPs in each territory by the total number of births in each territory reported to the National Center for Health Statistics. For Guam, Northern Mariana Islands, and Puerto Rico, we divided 2014 PHBPP data by the total number of births in each respective territory in 2014. For American Samoa and the US Virgin Islands, 2014 data were not available, so we used data from 2011 for American Samoa and from 2012 for the US Virgin Islands. For each territory, the prevalence range was a minimum and maximum determined from 2009-2014 PHBPP data; we excluded years with missing data (unpublished data from national PHBPP, National Center for Immunization and Respiratory Diseases, 2007-2014).

Non–US-Born Women

For infants born to non–US-born women, we estimated the HBsAg prevalence from the point prevalence and 95% CIs from CDC’s Enhanced Perinatal Hepatitis B Case Management Projects, which conducted enhanced identification of maternal-infant pairs and collected data on MCOB from 5 PHBPP sites (representing approximately 25% of the national program) from 2008-2012.²³ Prevalence estimates were for HBsAg-positive pregnant women.

Other/Unknown Country of Birth

For infants born to mothers whose country of birth was unknown, we used the HBsAg point prevalence and 95% CI calculated from NHANES for the other/unknown race/ethnicity subcategory.

Estimating Births to HBsAg-Positive Women

We multiplied each infant stratum categorized first by MCOB and then subcategorized them by either race/ethnicity or region by a point and range of HBsAg prevalence estimates as previously defined. We summed estimates for each stratum to obtain an overall estimate of annual births to HBsAg-positive women. We performed all analyses by using SAS version 9.3,²⁴ SAS-callable SUDAAN version 11.0.1,²⁵ and Microsoft Excel. Because we used de-identified data from existing data sets, CDC waived institutional review board approval.

Results

In 2015, the 50 states and the District of Columbia reported 3 978 497 births to women residing in the United States. Data on MCOB were available for 99.3% (3 950 648) births, with a range by state of 76.0% in Connecticut to nearly 100.0% in Montana. An estimated 20 678 (0.5%) births were to HBsAg-positive women. Infants of US-born women comprised 77.2% (n = 3 070 685) of all births and contributed 40.1% (8296 of 20 678) of estimated births to HBsAg-positive women. Infants of US territory–born women comprised 0.5% (n = 21 564) of total births and contributed 0.3% (63 of 20 678) of estimated births to HBsAg-positive women. Infants of non–US-born women comprised 21.5% (n = 857 105) of all births and contributed 57.9% (n = 11 981) of births to HBsAg-positive women. Infants of women whose country of birth was unknown comprised 0.7% (n = 29 143) of all births and contributed 1.6% (n = 338) of births to HBsAg-positive women (Table 2).

Table 2.

Number of births, HBsAg prevalence among women, and estimated number of births to HBsAg-positive women, by maternal country of birth, United States, 2015^a

Maternal Country of Birth Categoriesa	Births,a No. (%)	HBsAg Prevalence,b % (Range)	Estimated Births to HBsAg-Positive Women,c No. (Range) [%]
Total	3 978 497 (100.0)	—	20 678 (15 625-30 640) [0.5]
US-born
Total	3 070 685 (77.2)	—	8296 (4031-17 100) [40.1]
Non-Hispanic white	1 987 686 (64.7)	0.17 (0.07-0.39)	3379 (1391-7752) [40.7]
Non-Hispanic black	496 926 (16.2)	0.64 (0.37-1.13)	3180 (1839-5615) [38.3]
Hispanic	463 320 (15.1)	0.09 (0.03-0.24)	417 (139-1112) [5.0]
Asian/Pacific Islander	65 150 (2.1)	1.00 (0.52-1.91)	652 (339-1244) [7.9]
Other/unknown	57 603 (1.9)	1.16 (0.56-2.39)	668 (323-1377) [8.1]
US territory-born
Total	21 564 (0.5)	—	63 (36-81) [0.3]
American Samoa	900 (4.2)	2.55 (2.55-2.55)	23 (23-23) [36.5]
Guam	1564 (7.3)	1.18 (0.43 -1.55)	18 (7-24) [28.6]
Northern Mariana Islands	217 (1.0)	7.74 (1.17-7.74)	17 (3-17) [27.0]
Puerto Rico	17 983 (83.4)	0.02 (0.01-0.06)	4 (2-11) [6.3]
US Virgin Islands	900 (4.2)	0.14 (0.14-0.71)	1 (1-6) [1.6]
Non–US-born
Total	857 105 (21.5)	—	11 981 (11 395-12 762) [57.9]
Africad	64 228 (7.5)	3.42 (3.27-3.96)	2197 (2100-2543) [18.3]
Asia
East Asiae	66 384 (7.7)	8.73 (8.52-8.93)	5795 (5656-5928) [48.4]
South Asiaf	68 950 (8.0)	0.42 (0.37-0.47)	290 (255-324) [2.4]
Southeast Asiag	62 044 (7.2)	3.92 (3.76-4.08)	2432 (2333-2531) [20.3]
West/Central Asiah	9655 (1.1)	2.02 (1.72-2.32)	195 (166-224) [1.6]
Australia/Oceaniai	1892 (0.2)	0.19 (0-0.38)	4 (0-7) [0.03]
Caribbean (except Haiti)j	46 131 (5.4)	0.31 (0.28-0.34)	143 (129-157) [1.2]
Europe
Eastern Europek	32 397 (3.8)	0.59 (0.51-0.67)	191 (165-217) [1.6]
Southern Europel	10 337 (1.2)	1.39 (1.20 -1.57)	144 (124-162) [1.2]
Western and Northern Europem	25 492 (3.0)	0.16 (0.12-0.20)	41 (31-51) [0.3]
Haiti	13 160 (1.5)	1.10 (1.00 -1.20)	145 (132-158) [1.2]
Mexico and Central American	363 790 (42.4)	0.04 (0.03-0.04)	146 (109-146) [1.2]
Middle Easto	32 436 (3.8)	0.33 (0.27-0.38))	107 (88-123) [0.9]
North Americap	9859 (1.2)	0.05 (0.05-0.06)	5 (5-6) [0.04]
Pacific Islandsq	4283 (0.5)	1.58 (0.89-2.26)	68 (38-97) [0.6]
South Americar	46 067 (5.4)	0.17 (0.14-0.19)	78 (64-88) [0.7]
Other/unknowns	29 143 (0.7)	1.16 (0.56-2.39)	338 (163-697) [1.6]

Abbreviation: HBsAg, hepatitis B surface antigen.

^aData source: Unpublished data from 57 vital statistics jurisdictions, National Center for Health Statistics, 2015.

^bUS-born prevalence by race/ethnicity calculated from the National Health and Nutrition Examination Survey (NHANES) 2009-2014²²; range is a 95% confidence interval (CI). Prevalence estimates for non-Hispanic white, Hispanic, and other were based on <10 women with positive samples. US territory-born prevalences calculated from 2014 annual report data (infants born to HBsAg-positive women identified in territory divided by total births in territory) for Guam, Commonwealth of the Northern Mariana Islands, and Puerto Rico; 2012 annual report data for US Virgin Islands; and 2011 annual report data for American Samoa; the range is a minimum and maximum from 2009-2014 annual reports (years missing data were not included) (unpublished data from national Perinatal Hepatitis B Prevention Program [PHBPP], National Center for Immunization and Respiratory Diseases, 2007-2014). Foreign-born prevalences were from Walker et al²³; range is a 95% CI.

^cBirth estimates calculated by multiplying births in each category by corresponding HBsAg prevalence: estimated births to HBsAg-positive women = (number of infants in subcategory) × (HBsAg prevalence data from NHANES 2009-2014²² or PHBPP²³) (unpublished data from national PHBPP, National Center for Immunization and Respiratory Diseases, 2007-2014)). Births reported in 50 states and the District of Columbia were included in data; availability of maternal country of birth on infant birth certificates ranged from 76.0% (Connecticut) to 100.0% (Montana), with an overall known maternal country of birth of 99.3% in 2015.

^dAfrica includes Algeria, Angola, Bassas Da India, Benin, Botswana, Burkina Faso, Burundi, Cameroon, Cape Verde, Central African Republic, Chad, Comoros, Congo, Dahomey (Benin), Djibouti, Egypt, Equatorial Guinea, Eritrea, Ethiopia, Europa Island, French Territory of The Affars and Issas, Gabon, The Gambia, Ghana, Glorioso Islands, Guinea, Guinea-Bissau, Cote D’ Ivoire, Kenya, Lesotho, Liberia, Libya, Madagascar, Malawi, Mali, Mauritania, Mauritius, Mayotte, Morocco, Mozambique, Namibia, Niger, Nigeria, Reunion, Rwanda, Saint Helena, Sao Tome and Principe, Senegal, Seychelles, Sierra Leone, Somalia, South Africa, Southern Rhodesia, Spanish North Africa, Spanish Sahara, Sudan, Swaziland, Tanzania, Togo, Tromelin Island, Tunisia, Uganda, Western Sahara, Zambia, and Zimbabwe.

^eEast Asia includes China, Hong Kong, Japan, Macau, Mongolia, North Korea, South Korea, Southern Ryukyu Islands, and Taiwan

^fSouth Asia includes Bangladesh, Bhutan, India, Maldives, Nepal, Pakistan, Sikkim, and Sri Lanka.

^gSoutheast Asia includes Burma, Brunei, Cambodia, East Timor, Indonesia, Laos, Malaysia, Papua New Guinea, North Vietnam, Paracel Islands, Philippines, Singapore, South Vietnam Spratly Islands, Thailand, Timor, and Vietnam.

^hWest/Central Asia includes Afghanistan, Armenia, Azerbaijan, Georgia, Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan.

ⁱAustralia/Oceania includes Ashmore and Cartier Islands, Australia, Cocos (Keeling) Islands, Coral Sea Islands, New Zealand, and Norfolk Island.

^jCaribbean includes Anguilla, Antigua and Barbuda, Aruba, The Bahamas, Barbados, Bermuda, British Virgin Islands, Cayman Islands, Cuba, Dominica, Dominican Republic, Grenada, Guadeloupe, Jamaica, Martinique, Montserrat, Netherlands Antilles, Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, Swan Islands, Trinidad and Tobago, and Turks and Caicos Islands.

^kEastern Europe includes Belarus, Bulgaria, Czech Republic, Czechoslovakia, Estonia, Hungary, Latvia, Lithuania, Moldova, Poland, Romania, Russia, Slovakia, Ukraine, and Union of Soviet Socialist Republics.

^lSouthern Europe includes Albania, Andorra, Bosnia and Herzegovina, Croatia, F.Y.R.O. Macedonia, Gibraltar, Greece, Holy See (Vatican City), Italy, Malta, Portugal, San Marino, Slovenia, Spain, and Yugoslavia.

^mWestern and Northern Europe includes Austria, Belgium, Denmark, East Berlin, Finland, France, Guernsey, Germany, Iceland, Ireland, Isle of Man, Jan Mayen, Jersey, Liechtenstein, Luxembourg, Monaco, Netherlands, Norway, Svalbard, Sweden, Switzerland, United Kingdom, and West Berlin.

ⁿMexico and Central America includes Belize, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama, and Panama Canal Zone.

^oMiddle East includes Bahrain, Cyprus, Gaza Strip, Iran, Iraq, Israel, Jordan, Kuwait, Lebanon, Oman, Qatar, Saudi Arabia, Syria, Turkey, United Arab Emirates, West Bank, and Yemen.

^pNorth America includes Canada, Greenland, and Saint Pierre and Miquelon.

^qPacific Islands includes Canton and Enderberry Islands, Central and Southern Line Islands, Christmas Island, Clipperton Island, Cook Islands, Jarvis Island, Faroe Islands, Federated States of Micronesia, Fiji, French Polynesia, Gilbert and Ellice Islands, Gilbert Islands, Heard Island and Mcdonald Islands, Howland Island, Johnston Island, Juan De Nova Island, Kiribati, Marshall Islands, Midway Island, Nauru, New Caledonia, Niue, Palau, Palmyra Atoll, Pitcairn Island, Samoa, Solomon Islands, Tokelau, Tonga, Trust Territory of the Pacific Islands, Tuvalu, US Miscellaneous Pacific Islands, Vanuatu, Wallis and Futuna, and Wake Island.

^rSouth America includes Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Falkland Islands, French Guiana, Guyana, Paraguay, Peru, Suriname, Uruguay, and Venezuela.

^sOther/unknown includes Antarctica, Bouvet Island, British Indian Ocean Territory, French Southern and Antarctic Lands, South Georgia and The South Sandwich Islands, and unknown countries.

Of 8296 births to HBsAg-positive US-born women, the percentage of births was highest among non-Hispanic white (40.7%, n = 3379) and non-Hispanic black (38.3%, n = 3180) women; these groups comprised 64.7% (n = 1 987 686) and 16.2% (n = 496 926) of the 3 070 685 births to US-born women, respectively. Of 857 105 births to non–US-born women, women from Mexico and Central America gave birth to 42.4% (n = 363 790) of infants, and 1.2% (146 of 11 981) of these births were to HBsAg-positive women. The estimated percentage of births to HBsAg-positive women was highest in East Asia (48.4%, n = 5795), Southeast Asia (20.3%, n = 2432), and Africa (18.3%, n = 2197) (Table 2). Of all 20 678 births to HBsAg-positive women, the estimated percentage of births was highest among East Asian women (28.0%, n = 5795) and lowest among Australian/Oceanian women (0.03%, n = 4).

The MCOB model estimated 5666 fewer births to HBsAg-positive women in 2015 than estimated by the CDC race/ethnicity model (Table 3). During 2010-2015, both the race/ethnicity model and the MCOB model estimated an increasing number of births to HBsAg-positive pregnant women in the United States: from 24 223 to 26 344 in the racial/ethnic model and from 18 575 to 20 678 in the MCOB model. Although the point estimate was lower for the MCOB model than for the racial/ethnic model in each year examined, the estimated range in number of births around the MCOB point estimate included the point estimate using the racial/ethnic model.

Table 3.

Estimated number of births to HBsAg-positive women using 2 models, United States, 2010-2015^a

	Point Estimate (Range or Lower Limitb)
Model	2010	2011	2012	2013	2014	2015
Race/ethnicityc	24 223 (17 107)	24 589 (17 443)	25 912 (18 545)	25 268 (18 003)	26 444 (18 945)	26 344 (18 867)
Maternal country of birthd	18 575 (13 138-29 382)	18 962 (13 661-29 487)	19 989 (14 718-30 423)	19 721 (14 533-30 010)	21 062 (15 885-31 284)	20 678 (15 625-30 640)

Abbreviation: HBsAg, hepatitis B surface antigen.

^aData sources for building models include National Center for Health Statistics birth certificate data (unpublished data from 57 vital statistics jurisdictions, National Center for Health Statistics, 2010-2015), 2009-2014 National Health and Nutrition Examination Survey,²² and Perinatal Hepatitis B Prevention Program (unpublished data from national Perinatal Hepatitis B Prevention Program, National Center for Immunization and Respiratory Diseases, 2007-2014).²³

^bRange is only available as a lower limit for the race/ethnicity model because of data limitations.

^cModel currently used by the Centers for Disease Control and Prevention in which total annual births are multiplied by race- and ethnicity-specific HBsAg prevalence among women obtained from the 2009-2014 National Health and Nutrition Examination Survey, with the exception of Asian Pacific Islanders, for whom estimates were obtained from medical literature.¹²

^dModel categorizes total annual births primarily by mother’s country of birth and secondarily by race/ethnicity, territory of birth, or region of birth and multiplies each strata by category-specific HBsAg prevalence data obtained from the 2009-2014 National Health and Nutrition Examination Survey²² or Perinatal Hepatitis B Prevention Program (unpublished data from national Perinatal Hepatitis B Prevention Program, National Center for Immunization and Respiratory Diseases, 2007-2014).²³

Discussion

We found that births to non–US-born women represented a small proportion of all births in the United States but contributed to more than half of the estimated births to HBsAg-positive women, a finding supported by previous studies.^16,23 The estimated contribution of births to HBsAg-positive women varied widely by MCOB, which highlights the importance of incorporating MCOB in estimating annual births to HBsAg-positive women in the United States. The inclusion of data on MCOB on birth certificates increased to 99.3% in 2015, and this information was used in the MCOB model to determine annual estimates of infants at risk for perinatal HBV.

Our MCOB model differs from previously described models in several ways.^12,16 The current race/ethnicity model applies a single HBsAg prevalence to each broad race/ethnicity category without accounting for factors (eg, geographic origin) that could contribute to varying prevalence estimates within each group and, therefore, might not be representative of the population. For example, the non-Hispanic black category in the race/ethnicity model includes both African American women and women born in Africa, but HBsAg prevalence among black women born in Africa is estimated to be higher than that of black women born in the United States.^2,3,16 The CDC race/ethnicity model does not account for this disparity; as such, using a single HBsAg prevalence for a broad race/ethnicity category might not be representative of the population. In addition, although the race/ethnicity model separates US-born Asian/Pacific Islanders from non–US-born Asian/Pacific Islanders, the category is still broad and does not account for the widely varying HBsAg prevalence among various countries in Asia shown in the literature.² The MCOB model incorporates additional detail by substratifying MCOB into 16 geographic areas and uses more recent prevalence data, both of which attempt to address evolving HBsAg prevalence worldwide. Compared with the race/ethnicity model, the MCOB model yielded point estimates for fewer births to HBsAg-positive women, including 5666 fewer births in 2015.

The MCOB model, which was adapted from the method described by Din et al in 2011,¹⁶ differs from the model by Din et al in 3 important ways. First, the MCOB model separates US territory–born women from non–US-born women because US territories participate in the CDC-funded PHBPP and actively case-manage HBsAg-positive women and their infants to prevent mother-to-child transmission of HBV infection. Similarly, US-born women are assessed separately from Canadian-born women in the MCOB model. Second, in determining HBsAg prevalence estimates for categories, the MCOB model uses more recent NHANES data; the MCOB model also uses HBsAg prevalence estimates collected in recent years from PHBPPs that identified and case-managed HBsAg-positive pregnant women and their infants. These HBsAg prevalence estimates likely reflect the current US population more than prevalence estimates computed from the medical literature by Din et al. Third, the MCOB model incorporates data on MCOB from all US states and the District of Columbia, whereas Din et al were limited to applying data from only 22 states. These differences led to annual estimates of births to HBsAg-positive women that were lower when using the MCOB model (0.5% of all births) than when using the Din model (0.7% of all births).¹⁶ The HBsAg prevalence among non–US-born women used in the MCOB model provides a more in-depth perspective than recent literature^2,3,23 because these HBsAg prevalence estimates were calculated from 5 PHBPPs that conducted enhanced identification and case management of HBsAg-positive pregnant women.²³

Prevention of perinatal HBV infection is a goal of Healthy People 2020, CDC, and the US Department of Health and Human Services.^26,27 Key components include increasing coverage of HBV vaccine birth dose to 85% and reducing chronic HBV infections in children and infants to 400 cases.²⁷ The annual national estimate of births to HBsAg-positive women provides a marker of progress to these goals and assists PHBPP in planning surveillance, educational, and outreach activities to improve the identification of pregnant women and their infants, with the ultimate goal of preventing mother-to-child transmission of HBV infection. Our MCOB model estimates use granularity by MCOB, which provides an opportunity for PHBPP to target and improve screening and identification of pregnant HBsAg-positive women. The CDC-funded PHBPP typically identifies fewer than half of infants estimated to be born to HBsAg-positive women as projected by the current CDC race/ethnicity model. From 2000 to 2015, the race/ethnicity model determined that annual births to HBsAg-positive pregnant women increased, and this increase was attributed to a US population that was changing because of increased immigration.¹¹ The literature indicates that HBsAg prevalence among immigrants might more closely align with the HBsAG prevalence in their country of origin than in their country of relocation.^2,15,28 Unlike the race/ethnicity model, the MCOB model accounts for both MCOB and updated yet evolving HBsAg prevalence in various regions of the world.

In 1992, the World Health Organization recommended that all countries integrate hepatitis B vaccine, which can help prevent mother-to-child transmission of hepatitis B, into childhood immunization schedules²⁰; however, birth-dose implementation has lagged in several areas, with a global coverage of 43% in 2017.^29,30 Both national serosurveys in endemic countries and US-based assessments can inform and update HBsAg prevalence estimates based on MCOB. Because global vaccine programs affect hepatitis B prevalence, the MCOB model can be used as a framework to incorporate these evolving HBsAg prevalences for women from various parts of the world; this model enables PHBPPs to set a benchmark for identifying annual births to HBsAg-positive women with granularity in MCOB and assessing progress in reaching US elimination goals.³¹

Limitations

This study had several limitations to the HBsAg prevalence estimates used in the MCOB models. First, research demonstrates the effect of country of origin on HBV prevalence,^2,4,15,28 including a wide range in global HBV prevalence by country⁴ and a higher than previously estimated number of non–US-born persons infected with chronic hepatitis B living in the United States.² We used country of birth in our MCOB estimates; however, we were unable to test the validity of our MCOB estimates because of the lack of a gold standard for this estimation. Second, to comprehensively determine HBsAg prevalence among women from various parts of the world, we used multiple data sources and data from various years depending on source; these differences could have affected the number of estimated births. Third, NHANES data used to determine HBsAg prevalence among women born in the United States have several limitations that could also affect estimates of births to HBsAg-positive women. NHANES is believed to underestimate overall HBsAg prevalence because the study population does not include certain high-risk groups, such as persons who are institutionalized, incarcerated, or homeless.^{2,22,26,32,33} The sample size in NHANES was also limited, and it was not possible to calculate prevalence by race/ethnicity and childbearing age for US-born women only. Therefore, the prevalences used to estimate births to US-born women used HBsAg prevalence among US women of all ages (including both US-born and non–US-born women). In addition, fewer than 10 HBsAg-positive samples were available in NHANES for each of the non-Hispanic white, Hispanic, and other race/ethnicity groups. This limited sample size was particularly challenging for determining prevalence estimates for the other race/ethnicity group, which included American Indians, Alaska Natives, and persons of unknown race/ethnicity. Because of the limitations of NHANES data, the MCOB model may have overestimated or underestimated the number of births to HBsAg-positive women born in the United States.

Fourth, we used PHBPP data collected from annual programmatic reports to determine HBsAg prevalence among US territory–born women (unpublished data from national PHBPP, National Center for Immunization and Respiratory Diseases, 2007-2014), and we used PHBPP data collected through the Enhanced Perinatal Hepatitis B Case Management Projects to determine prevalence among non–US-born women.²³ Overall, the PHBPP is believed to underidentify infants born to HBsAg-positive women, and the resulting HBsAg prevalences are likely underestimated. Therefore, the MCOB model might also underestimate the number of births to HBsAg-positive women born outside the 50 states and the District of Columbia.

Conclusions

The MCOB model categorizes infants by MCOB and then either race/ethnicity or region, which allows for applying category-specific HBsAg prevalence estimates to estimate at-risk infants. This granularity aligns with the literature demonstrating the importance of country of birth in HBsAg prevalence^{2,3,15,16,28,34} and provides a contemporary estimate of HBV-affected maternal-infant pairs that can be used to inform national public health programmatic decisions and response to prevent mother-to-child transmission of HBV infection.