Bio

Academic Appointments


Professional Education


  • Postdoctoral Fellow, Stanford University, Epidemiology, Infectious Diseases (2011)
  • MS, Stanford University, Epidemiology (2007)
  • Board Certification, ABIM, Infectious Diseases (2005)
  • Fellowship, Stanford University, Infectious Diseases (2005)
  • Board Certification, ABIM, Internal Medicine (2002)
  • Residency, Brigham and Women's Hospital, Internal Medicine (2002)
  • MD, UCSF, Medicine (1999)

Research & Scholarship

Current Research and Scholarly Interests


I study infectious diseases in marginalized and vulnerable populations, with a specific focus on gastrointestinal infections and tuberculosis. My projects include assessing outcomes in patients, elucidating determinants of active tuberculosis, and studying the effects of chronic disease and co-infections and host immune response.

Publications

Journal Articles


  • House calls by community health workers and public health nurses to improve adherence to isoniazid monotherapy for latent tuberculosis infection: a retrospective study BMC PUBLIC HEALTH Chang, A. H., Polesky, A., Bhatia, G. 2013; 13
  • The immune response to tuberculosis infection in the setting of Helicobacter pylori and helminth infections. Epidemiology and infection Perry, S., Chang, A. H., Sanchez, L., Yang, S., Haggerty, T. D., Parsonnet, J. 2013; 141 (6): 1232-1243

    Abstract

    We screened 176 healthy, adult (aged 18-55 years) US refugees from tuberculosis (TB)-endemic countries to evaluate whether cytokine responses to latent TB infection (LTBI) are modified in the setting of concurrent H. pylori and helminth infection. As measured by the Quantiferon-TB GOLD interferon-? release assay, a total 38 (22%) subjects had LTBI, of which 28 (74%) also were H. pylori seropositive and/or helminth infected. Relative to ten subjects with LTBI only, 16 subjects with concurrent H. pylori infection had significantly elevated levels of IFN-?, and nine subjects with both H. pylori and helminth infection had significantly elevated levels of IFN-?, IL-2, IL-13, and IL-5. H. pylori is associated with enhanced IFN-? responses to TB, even in the setting of concurrent helminth infection. Efficacy of TB vaccines may vary with the co-existence of these three infections in the developing world.

    View details for DOI 10.1017/S0950268812001823

    View details for PubMedID 22954328

  • Decreasing Intestinal Parasites in Recent Northern California Refugees AMERICAN JOURNAL OF TROPICAL MEDICINE AND HYGIENE Chang, A. H., Perry, S., Du, J. N., Agunbiade, A., Polesky, A., Parsonnet, J. 2013; 88 (1): 191-197

    Abstract

    Beginning in 2005, the Centers for Disease Control and Prevention (CDC) expanded the overseas presumptive treatment of intestinal parasites with albendazole to include refugees from the Middle East. We surveyed the prevalence of helminths and protozoa in recent Middle Eastern refugees (2008-2010) in comparison with refugees from other geographical regions and from a previous survey (2001-2004) in Santa Clara County, California. Based on stool microscopy, helminth infections decreased, particularly in Middle Eastern refugees (0.1% versus 2.3% 2001-2004, P = 0.01). Among all refugees, Giardia intestinalis was the most common protozoan found. Protozoa infections also decreased somewhat in Middle Eastern refugees (7.2%, 2008-2010 versus 12.9%, 2001-2004, P = 0.08). Serology for Strongyloides stercoralis and Schistosoma spp. identified more infected individuals than stool exams. Helminth infections are increasingly rare in refugees to Northern California. Routine screening stool microscopy may be unnecessary in all refugees.

    View details for DOI 10.4269/ajtmh.2012.12-0349

    View details for Web of Science ID 000313757500031

    View details for PubMedID 23149583

  • Effect of Helicobacter pylori Infection on Symptoms of Gastroenteritis Due to Enteropathogenic Escherichia coli in Adults DIGESTIVE DISEASES AND SCIENCES Chang, A. H., Haggerty, T. D., de Martel, C., Leung, C. W., Parsonnet, J. 2011; 56 (2): 457-464

    Abstract

    Helicobacter pylori can cause hypochlorhydria in some hosts and predispose to diarrheal infections.We tested the hypothesis that chronic H. pylori infection increases the risk of diarrheal illness due to an acid-sensitive organism: enteropathogenic Escherichia coli (EPEC).After testing healthy adult volunteers for H. pylori, 19 infected and 26 uninfected subjects had gastric pH probes placed and were given 5-10 × 10(9) EPEC organisms; six had previously received a proton pump inhibitor. We measured diarrhea and created a composite gastroenteritis severity score based on symptoms in the 48 h following exposure. Outcomes were compared using logistic regression and analysis of covariance.More H. pylori-infected (36.8%) than H. pylori-uninfected subjects (7.7%) were hypochlorhydric (P = 0.02). Six (31.6%) H. pylori-infected and five H. pylori-uninfected subjects (19.2%) developed diarrhea (P = 0.34). Hypochlorhydria was a strong risk factor for diarrhea [odds ratio (OR) 6.25, confidence interval (CI): 1.29-30.35]. After adjusting for hypochlorhydria and EPEC dose, H. pylori was not associated with diarrhea (OR 0.89, CI: 0.17-4.58). Among those with symptoms, H. pylori-infected subjects had lower gastroenteritis severity score than did H. pylori-uninfected subjects (2.6, CI: 1.9-3.4 versus 1.5, CI: 1.1-1.9, P = 0.01), particularly if they were also hypochlorhydric (3.8, CI: 2.3-5.3 versus 1.9, CI: 1.3-2.5, P = 0.02).In adults, H. pylori infection was associated with hypochlorhydria but had no detectable effect on occurrence of diarrhea. Among symptomatic subjects, H. pylori infection decreased severity of gastroenteritis.

    View details for DOI 10.1007/s10620-010-1309-z

    View details for Web of Science ID 000286664900025

    View details for PubMedID 20635147

  • Local epidemic history as a predictor of tuberculosis incidence in Saskatchewan aboriginal communities International Journal of Tuberculosis and Lung Disease Pepperell C*, Chang AH*, Wobeser W, Parsonnet J, Hoeppner VH. *Equal contributions 2011; 15 (7): 899-905
  • Role of Bacteria in Oncogenesis CLINICAL MICROBIOLOGY REVIEWS Chang, A. H., Parsonnet, J. 2010; 23 (4): 837-?

    Abstract

    Although scientific knowledge in viral oncology has exploded in the 20th century, the role of bacteria as mediators of oncogenesis has been less well elucidated. Understanding bacterial carcinogenesis has become increasingly important as a possible means of cancer prevention. This review summarizes clinical, epidemiological, and experimental evidence as well as possible mechanisms of bacterial induction of or protection from malignancy.

    View details for DOI 10.1128/CMR.00012-10

    View details for Web of Science ID 000282635900006

    View details for PubMedID 20930075

  • Cost-Effectiveness of a Potential Prophylactic Helicobacter pylori Vaccine in the United States JOURNAL OF INFECTIOUS DISEASES Rupnow, M. F., Chang, A. H., Shachter, R. D., Owens, D. K., Parsonnet, J. 2009; 200 (8): 1311-1317

    Abstract

    Helicobacter pylori vaccines are under development to prevent infection. We quantified the cost-effectiveness of such a vaccine in the United States, using a dynamic transmission model.We compartmentalized the population by age, infection status, and clinical disease state and measured effectiveness in quality-adjusted life years (QALYs). We simulated no intervention, vaccination of infants, and vaccination of school-age children. Variables included costs of vaccine, vaccine administration, and gastric cancer treatment (in 2007 US dollars), vaccine efficacy, quality adjustment due to gastric cancer, and discount rate. We evaluated possible outcomes for periods of 10-75 years.H. pylori vaccination of infants would cost $2.9 billion over 10 years; savings from cancer prevention would be realized decades later. Over a long time horizon (75 years), incremental costs of H. pylori vaccination would be $1.8 billion, and incremental QALYs would be 0.5 million, yielding a cost-effectiveness ratio of $3871/QALY. With school-age vaccination, the cost-effectiveness ratio would be $22,137/QALY. With time limited to <40 years, the cost-effectiveness ratio exceeded $50,000/QALY.When evaluated with a time horizon beyond 40 years, the use of a prophylactic H. pylori vaccine was cost-effective in the United States, especially with infant vaccination.

    View details for DOI 10.1086/605845

    View details for Web of Science ID 000270089400018

    View details for PubMedID 19751153

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