title: Incidence of Severe and Nonsevere Pertussis Among HIV-Exposed and -Unexposed Zambian Infants Through 14 Weeks of Age: Results From the Southern Africa Mother Infant Pertussis Study (SAMIPS), a Longitudinal Birth Cohort Study.
abstract: BACKGROUND
  Maternal vaccination with tetanus, reduced-dose diphtheria, and acellular pertussis vaccine (Tdap) could be an effective way of mitigating the high residual burden of infant morbidity and mortality caused by Bordetella pertussis To better inform such interventions, we conducted a burden-of-disease study to determine the incidence of severe and nonsevere pertussis among a population of Zambian infants.
  
  
  METHODS
  Mother-infant pairs were enrolled at 1 week of life, and then seen at 2- to 3-week intervals through 14 weeks of age. At each visit, nasopharyngeal (NP) swabs were obtained from both, and symptoms were catalogued. Using polymerase chain reaction (PCR) to identify cases, and a severity scoring system to triage these into severe/nonsevere, we calculated disease incidence using person-time at risk as the denominator.
  
  
  RESULTS
  From a population of 1981 infants, we identified 10 with clinical pertussis, for an overall incidence of 2.4 cases (95% confidence interval [CI], 1.2-4.2) per 1000 infant-months and a cumulative incidence of 5.2 cases (95% CI, 2.6-9.0) per 1000 infants. Nine of 10 cases occurred within a 3-month window (May-July 2015), with highest incidence between birth and 6 weeks of age (3.5 cases per 1000 infant-months), concentrated among infants prior to vaccination or among those who had only received 1 dose of Diphtheria Tetanus whole cell Pertussis (DTwP). Maternal human immunodeficiency virus (HIV) modestly increased the risk of infant pertussis (risk ratio, 1.8 [95% CI, .5-6.9]). Only 1 of 10 infant cases qualified as having severe pertussis. The rest presented with the mild and nonspecific symptoms of cough, coryza, and/or tachypnea. Notably, cough durations were long, exceeding 30 days in several cases, with PCRs repeatedly positive over time.
  
  
  CONCLUSIONS
  Pertussis is circulating freely among this population of Zambian infants but rarely presents with the classical symptoms of paroxysmal cough, whooping, apnea, and cyanosis. Maternal HIV appears to increase the risk, while lack of effective exposure to DTwP increased the risk.
authors.affiliation: Center for Global Health and Development.|Department of Global Health, Boston University School of Public Health, Massachusetts.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Gill
authors.affiliation: Center for Global Health and Development.|Department of Global Health, Boston University School of Public Health, Massachusetts.|Zambia Center for Applied Health Research and Development.
authors.forename: Lawrence
authors.initials: L
authors.lastname: Mwananyanda
authors.affiliation: Center for Global Health and Development.|Department of Global Health, Boston University School of Public Health, Massachusetts.
authors.forename: William
authors.initials: W
authors.lastname: MacLeod
authors.affiliation: Zambia Center for Applied Health Research and Development.|Department of Biomedical Sciences, School of Medicine, University of Zambia, Lusaka.
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Kwenda
authors.affiliation: Zambia Center for Applied Health Research and Development.
authors.forename: Magdalene
authors.initials: M
authors.lastname: Mwale
authors.affiliation: Center for Global Health and Development.|Department of Global Health, Boston University School of Public Health, Massachusetts.
authors.forename: Anna L
authors.initials: AL
authors.lastname: Williams
authors.affiliation: Zambia Center for Applied Health Research and Development.
authors.forename: Kazungu
authors.initials: K
authors.lastname: Siazeele
authors.affiliation: Data Coordinating Center, Boston University School of Public Health, Massachusetts.
authors.forename: Zhaoyan
authors.initials: Z
authors.lastname: Yang
authors.affiliation: Zambia Center for Applied Health Research and Development.|Department of Pathology and Microbiology, University Teaching Hospital, Lusaka, Zambia.
authors.forename: James
authors.initials: J
authors.lastname: Mwansa
authors.affiliation: Center for Global Health and Development.|Department of Global Health, Boston University School of Public Health, Massachusetts.
authors.forename: Donald M
authors.initials: DM
authors.lastname: Thea
mesh_terms: D000328:Adult; D000353:Africa, Southern / Q000453:epidemiology; D001886:Bordetella pertussis / Q000235:genetics; D015331:Cohort Studies; D060085:Coinfection; D003430:Cross-Sectional Studies; D004781:Environmental Exposure / Q000009:adverse effects; D005260:Female; D015658:HIV Infections / Q000453:epidemiology*; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D008137:Longitudinal Studies; D008297:Male; D008403:Mass Screening; D010567:Pertussis Vaccine / Q000276:immunology; D011159:Population Surveillance; D012307:Risk Factors; D012621:Seasons; D012720:Severity of Illness Index; D014611:Vaccination; D014917:Whooping Cough / Q000175:diagnosis / Q000453:epidemiology*; D055815:Young Adult
chemical_list: D010567:Pertussis Vaccine
keywords: Bordetella pertussis; cohort study; incidence; prospective surveillance; whooping cough