the outbreak was brought to the attention of health officials when local emergency medicine physicians noticed a significant increase in cases of hepatitis a in the county. after conducting its investigation, the cdc attributed the source of the outbreak to the use of contaminated raw green onion. the restaurant was purchasing its green onion stock from farms in mexico at the time. it is believed that the green onions may have been contaminated through the use of contaminated water for crop irrigation, rinsing, or icing or by handling of the vegetables by infected people. green onion had caused similar outbreaks of hepatitis a in the southern united states prior to this, but not to the same magnitude. the cdc believes that the restaurant's use of a large communal bucket for chopped raw green onion allowed non-contaminated plants to be mixed with contaminated ones, increasing the number of vectors of infection and amplifying the outbreak. the restaurant was closed once it was discovered to be the source, and over 9,000 people were given hepatitis a immune globulin because they had either eaten at the restaurant or had been in close contact with someone who had. special populations hiv co-infection persons infected with hiv have a particularly high burden of hiv-hcv co-infection. in a recent study by the who, the likelihood of being infected with hepatitis c virus was six times greater in those who also had hiv. the prevalence of hiv-hcv co-infection worldwide was estimated to be 6.2% representing more than 2.2 million people. intravenous drug use was an independent risk factor for hcv infection. in the who study, the prevalence of hiv-hcv co-infection was markedly higher at 82.4% in those who injected drugs compared to the general population (2.4%). in a study of hiv-hcv co-infection among hiv positive men who have sex with men (msm), the overall prevalence of anti-hepatitis c antibodies was estimated to be 8.1% and increased to 40% among hiv positive msm who also injected drugs. hepatitis b vertical transmission is a significant contributor of new hbv cases each year, with 35–50% of transmission from mother to neonate in endemic countries. vertical transmission occurs largely via a neonate's exposure to maternal blood and vaginal secretions during birth. while the risk of progression to chronic infection is approximately 5% among adults who contract the virus, it is as high as 95% among neonates subject to vertical transmission. the risk of viral transmission is approximately 10–20% when maternal blood is positive for hbsag, and up to 90% when also positive for hbeag. given the high risk of perinatal transmission, the cdc recommends screening all pregnant women for hbv at their first prenatal visit. it is safe for non-immune pregnant women to receive the hbv vaccine. based on the limited available evidence, the american association for the study of liver diseases (aasld) recommends antiviral therapy in pregnant women whose viral load exceeds 200,000 iu/ml. a growing body of evidence shows that antiviral therapy initiated in the third trimester significantly reduces transmission to the neonate. a systematic review of the antiretroviral pregnancy registry database found that there was no increased risk of congenital anomalies with tenofovir; for this reason, along with its potency and low risk of resistance, the aasld recommends this drug. a 2010 systematic review and meta-analysis found that lamivudine initiated early in the third trimester also significantly reduced mother-to-child transmission of hbv, without any known adverse effects. the acog states that the evidence available does not suggest any particular mode of delivery (i.e. vaginal vs. cesarean) is better at reducing vertical transmission in mothers with hbv. the who and cdc recommend that neonates born to mothers with hbv should receive hepatitis b immune globulin (hbig) as well as the hbv vaccine within 12 hours of birth. for infants who have received hbig and the hbv vaccine, breastfeeding is safe. hepatitis c estimates of the rate of hcv vertical transmission range from 2–8%; a 2014 systematic review and meta-analysis found the risk to be 5.8% in hcv-positive, hiv-negative women. the same study found the risk of vertical transmission to be 10.8% in hcv-positive, hiv-positive women. other studies have found the risk of vertical transmission to be as high as 44% among hiv-positive women. the risk of vertical transmission is higher when the virus is detectable in the mother's blood. evidence does not indicate that mode of delivery (i.e. vaginal vs. cesarean) has an effect on vertical transmission. for women who are hcv-positive and hiv-negative, breastfeeding is safe. cdc guidelines suggest avoiding it if a woman's nipples are cracked or bleeding to reduce the risk of transmission. hepatitis e pregnant women who contract hev are at significant risk of developing fulminant hepatitis with maternal mortality rates as high as 20–30%, most commonly in the third trimester . a 2016 systematic review and meta-analysis of 47 studies that included 3968 people found maternal case-fatality rates (cfr) of 20.8% and fetal cfr of 34.2%; among women who developed fulminant hepatic failure, cfr was 61.2%.