Cohort profile: China respiratory illness surveillance among pregnant women (CRISP), 2015-2018.

PURPOSE: We established the China Respiratory Illness Surveillance among Pregnant women (CRISP) to conduct active surveillance for influenza-associated respiratory illness during pregnancy in China from 2015 to 2018. Among annual cohorts of pregnant women, we assess the incidence of acute respiratory illness (ARI), influenza-like illness (ILI), laboratory-confirmed influenza virus infection and the seroconversion proportion during the winter influenza season. We also plan to examine the effect of influenza virus infection on adverse pregnancy, delivery and infant health outcomes with cumulative data from the three annual cohorts.

PARTICIPANTS: Cohort nurses enrol pregnant women in different trimesters of pregnancy from prenatal care facilities in Suzhou, Jiangsu Province, eastern China. Pregnant women who plan to deliver in the study facilities are eligible. Pregnant women who are seeking care for anything other than routine prenatal care, such as confirmation of low progesterone and threatened miscarriage, are excluded. At enrolment, study nurses collect baseline information on demographics, education-level attained, underlying medical conditions, seasonal influenza vaccination receipt, risk factors for influenza infection, gravidity and parity and contact information. For each participant, cohort nurses conduct twice weekly follow-up contacts, one phone call and one WeChat message (free instant messaging), from the time of enrolment until delivery or termination of pregnancy. During follow-up, study nurses ask about symptoms, timing and characteristics of ARI, healthcare-seeking behaviour and medications taken for participants reporting respiratory illness since the last contact. In addition, we collect combined nasal and throat swabs for identified ARI to test for influenza viruses. We collect paired sera before and after the influenza season. Active respiratory illness surveillance and seroinfection data during pregnancy of participants are linked to their medical record and the Suzhou Maternal Child Information System for detailed information on clinical treatment for respiratory illness, pregnancy, delivery and infant health outcomes.

FINDINGS TO DATE: In 2015-2016, of 4915 pregnant women approached, 192 (4%) refused to participate, 91 (2%) were ineligible because they did not plan to deliver in one of the study hospitals or because their visit was for anything other than routine prenatal care and 4632 (94%) were enrolled, 46% during their first trimester of pregnancy (range 5-12 weeks), 48% during the second trimester (range 13-27 weeks) and 6% during the third trimester (range 28-37 weeks). The median age of the enrollees was 27 years (range 16-45) and two (0.04%, 95% CI 0.01% to 0.17%) reported influenza vaccination in the previous 12 months before pregnancy, while zero reported influenza vaccination in the previous 12 months during pregnancy. During the observation time of 648 518 person-days, 1355 ARI episodes were identified. Among 1127 swabs collected (for 83% of all ARIs), 68 (6%) tested positive for influenza virus, for a laboratory-confirmed influenza incidence of 0.31 (95% CI 0.25 to 0.40) per 100 person-months during pregnancy in the study cohort.

FUTURE PLANS: Results will be used to describe influenza disease burden in this population to model potential numbers of influenza illnesses averted if influenza vaccination coverage were increased and to support enhanced influenza prevention and control strategies among pregnant women in China. We also plan to enrol and follow three cohorts of pregnant women over three influenza seasons during 2015-2018 which will allow an analysis of the effect of influenza virus infection during pregnancy on adverse pregnancy, delivery and infant outcomes.