Burden of Influenza and Respiratory Syncytial Virus Infection in Pregnant Women and Infants Under 6 Months in Mongolia: A Prospective Cohort Study

Abstract

BackgroundPregnant women and infants under 6 months are at risk of influenza-related complications. Limited information exists on their community burden of respiratory viruses.Methods and FindingsThis prospective, observational open cohort study was conducted in Baganuur district, Ulaanbaatar, Mongolia during 2013/14 and 2014/15 influenza seasons. Influenza-like illness (ILI) and severe acute respiratory infection (sARI) were identified by follow-up calls twice a week. For those identified, influenza and respiratory syncytical virus (RSV) were tested by point-of-care test kits. We calculated overall and stratified (by trimester or age group) incidence rates (IR) and used Cox proportional hazard regression for risk factor analyses. Among 1260 unvaccinated pregnant women enrolled, overall IRs for ILI, sARI and influenza A were 11.8 (95% confidence interval (C.I):11.2–12.4), 0.1 (95%C.I:0.0–0.4), and 1.7 (95%C.I:1.5–1.9) per 1,000person-days, respectively. One sARI case was influenza A positive. IRs and adjusted hazard ratios (Adj.HR) for ILI and influenza A were lowest in the third trimester. Those with co-morbidity were 1.4 times more likely to develop ILI [Adj.HR:1.4 (95%C.I:1.1–1.9)]. Among 1304 infants enrolled, overall ILI and sARI IRs were 15.2 (95%C.I:14.5–15.8) and 20.5 (95%C.I:19.7–21.3) per 1,000person-days, respectively. From the tested ILI (77.6%) and sARI (30.6%) cases, the overall positivity rates were 6.3% (influenza A), 1.1% (influenza B) and 9.3% (RSV). Positivity rates of influenza A and RSV tend to increase with age. sARI cases were 1.4 times more likely to be male [Adj.HR:1.4 (95%C.I:1.1–1.8)]. Among all influenza A and RSV positive infants, 11.8% and 68.0% were respectively identified among sARI hospitalized cases.ConclusionWe observed low overall influenza A burden in both groups, though underestimation was likely due to point-of-care tests used. For infants, RSV burden was more significant than influenza A. These findings would be useful for establishing control strategies for both viruses in Mongolia.

Clinical characteristics and outcomes of respiratory syncytial virus infection in pregnant women

“…Cough, congestion, and sore throat were the most common symptoms among those with PCRconfirmed RSV. In previous studies of ILI, pregnant women with RSV generally reported a mild, febrile illness restricted to the upper airways [14,15]. In our study women who reported fever also had symptoms of LRTI.…”

“…An RSV attack rate as high as 13% (10/77) is estimated if calculated using the first ARI episode. This is substantial given that the RSV season in Houston was relatively mild compared to previous years [28], and greater than reported by maternal studies of respiratory illness in Nepal and Mongolia, where RSV accounted for 2% and 2.4% of ARI cases, respectively [14,15]. However, because fever was an inclusion criteria for those studies, and fever occurs in less than one-third of adult RSV infections, these numbers may be an underestimate [29].…”

“…Due to differences in study design and sample collection, it is difficult to make comparisons between our study and others that have documented maternal RSV infection. Three of the previous studies were prospective, wherein a participant was actively followed during the RSV season by weekly visits or telephone calls, sampled when she became ill, and followed for clinical outcomes through the duration of her pregnancy [14][15][16]. However, these study participants were only sampled when they reported ILI or sought medical attention for their respiratory illness.…”

“…A case-series study was the first to describe severe RSV infection during pregnancy: two of the three cases were hospitalized and required mechanical ventilation [13]. In addition, several large prospective maternal cohort studies of influenza-like illness (ILI) evaluated during influenza vaccine trials have described maternal RSV infection incidences of 3.9/1000 person-years in Nepal, 5.3/1000 person-months in South Africa, and 0.3/1000 persondays in Mongolia [14][15][16]. Recently, a retrospective multicountry study of ARI-related hospitalizations among pregnant women identified 846 women who were tested for RSV during the influenza season, 21 (2.5%) had detectable RSV by real-time reverse transcription polymerase chain reaction (PCR) [17].…”

Respiratory syncytial virus

“…Most studies of RSV infection or disease during pregnancy are based on case reports or secondary analyses of influenza vaccine trials [15][16][17]. A recent prospective longitudinal community based study conducted in Houston, Texas, provides additional information regarding the epidemiology of RSV and other respiratory viruses in healthy pregnant women receiving prenatal care at a community obstetrical clinic [18].…”