Association between seasonal influenza vaccination in 2008-2009 and pandemic influenza A (H1N1) 2009 infection among school students from Kobe, Japan, April-June 2009.

We assessed the effect of seasonal trivalent inactivated influenza vaccination (TIV) on pandemic influenza 2009 (pH1N1)-related illness from April to June 2009 among 2849 students (aged 12-18 years). TIV was associated with an increase in the frequency of pH1N1-related illness among subjects (adjusted odds ratio, 1.47; 95% confidence interval, 1.14-1.89). TIV during the 2008-2009 season increased the risk of pH1N1-related illness from April to June 2009.

[Field epidemiology investigation on measles outbreak started from a junior high school at Kita Ibaraki City].

We studied measles outbreak in Ibaraki Prefecture in spring 2002 as members of Field Epidemiology Training Program Japan (FETPJ). Of 84 cases diagnosed by not laboratory test but clinically, 67 (79.8%) were junior high school students, 9 (10.7%) were other students, and 8 (9.5%) were ordinary adult and infant citizens. Of the 84, 46 (54.8%) had been vaccinated. Most did not show typical Koplik spots. The city in which the school was located promoted vaccinations for infants and children aged 7.5 years old to grade 1 in High school. Questionnaire given to junior high students were detected 86 cases, of whom 57 (66.3%) were male. Overall, 4 peaks of clusters were observed in an epidemic curve, among which graduates' farewell parties and graduation ceremonies were the most common opportunities for measles virus exposure. The overall vaccination rate at school was 82.2%, vaccine efficacy extremely low at 72.5%, and vaccine failure high at 15.2%. Symptoms among those vaccinated were significantly milder than those not vaccinated. Immunity of those vaccinated as infants may have been decreased due to scarcity of measles cases in the last 10 years. In such situations--much less in typical measles among susceptible non affected and non vaccinated subjects--atypical or mild measles may be difficult to diagnose. These findings may keep clarify the need to introduce two-dose measles immunization in Japan.

[Outpatient antimicrobial drug use and antimicrobial resistance frequency in Suwa area, Nagano, Japan].

A cross-sectional study was conducted to determine antimicrobial use and to analyze the correlation to resistant bacteria. Records on antimicrobial prescriptions in Suwa area, Nagano prefecture, were collected from December 2009 to May 2010 from a national health insurance database system. Records on antimicrobial-resistant bacteria during the same period were collected from area hospitals. Data was then compared to data published in Europe. The target population was 31,505, or 27.1% of the total area population. More antimicrobials were prescribed in an outpatient setting rather for inpatients. Total outpatient antimicrobial use was 9.34 defined daily dose (DDD) per 1,000 subject days. Macrolides, lincosamides, and streptogramins (MLS) was the most prescribed drug group, followed by beta-lactams other than penicillin and quinolone. The quinolone-resistance rate among Escherichia coli in this area was within a predictable range based on European data, although that of macrolide-resistance among Streptococcus pneumoniae exceeded the predictable range. The health insurance system electronic database proved useful in collecting data on antimicrobial use for curbing action against antimicrobial resistance, including antimicrobial stewardship.

Risk factors for severe hand foot and mouth disease.

BACKGROUND: Hand foot and mouth disease (HFMD) and herpangina are enteroviral infectious diseases caused mainly by Coxsackie virus A (CA) or enterovirus 71 (EV71). From 2000 to 2002, many complicated cases were reported in Japan, therefore a nationwide questionnaire survey was carried out to assess the situation. The subjects were patients with HFMD or herpangina, or other enterovirus infection from 2000 to 2002, who were either hospitalized over 24 h or who died. The response rates were 41.3% in 2000 and 2001 and 31.6% in 2002. The survey period included the year 2000, when HFMD epidemics due to EV71 occurred. To examine risk factors causing complications of enterovirus infection, severe cases of HFMD were focused on. METHODS: HFMD cases in 2000 were divided into two groups according to severity: 'more severe' and 'less severe'. 'More severe' was defined as 'fatal, involving sequelae, or involving hospitalization for 7 days or longer'. Statistical analyses were conducted with Epi info version 3.3 and the association between risk factors and severity was estimated. RESULTS: The number of patients with more severe and less severe cases was 96 and 103, respectively. There was no difference in sex, age, having siblings and family history between the two groups. There was a significant association between attending child care center and severe HFMD. CONCLUSIONS: It is not clear why attending child care centers was associated with HFMD severity. Further study is needed.

Seasonal influenza surveillance using prescription data for anti-influenza medications.

Surveillance is critical for both early detection and a timely public health response to infectious diseases. Electronic information systems have been widely adopted by pharmacies in Japan. The aim of this study is to evaluate the feasibility of using prescription data for influenza surveillance in Japan to facilitate the development of a daily reporting system. This is a retrospective study using questionnaires mailed to pharmacies in Sakai City, Osaka, Japan in October 2007. The total number of prescriptions for oseltamivir and zanamivir and the number of influenza cases reported by sentinel surveillance in Sakai during the investigation period showed excellent correlation, with a correlation coefficient of 0.954. Further analysis showed that the data from as few as eight pharmacies result in a correlation coefficient of 0.9. These results demonstrate the feasibility of such a system and that pharmacy prescription data are a very useful indicator of sentinel surveillance for influenza.

Estimation of measles vaccine coverage needed to prevent transmission in schools.

BACKGROUND: The aim of the present study was to produce the first estimation in Japan of the basic reproduction number (R(0)) and the minimum level of vaccine coverage needed to prevent measles outbreaks (P(c)). METHODS: A questionnaire survey was conducted during two measles outbreaks among 12-15-year-old middle school students in one prefecture in spring, from the end of February to the beginning of May 2002, and a stochastic mathematical model was constructed to calculate vaccine effectiveness (VE) and the basic reproduction number (R(0)). P(c) was calculated from R(0) and VE. RESULTS: In outbreak 1 (school A), 62 (94%) of 66 patients responded to the questionnaire. Of a total of 601 students, 534 (88.9%) responded. Of these, 82.6% (441/534) had previously received measles vaccine. In outbreak 2 (school B), 20 (99%) of 21 patients responded. Of a total of 375 students, 373 (99.5%) responded. Of these, 317 (85.0%) received measles immunization. Mathematical analysis was as follows: in outbreak 1 R(0) was 7.40 (95% confidence interval [CI]: 7.36-7.44) and VE was 76.55% (95%CI: 53.24-87.54). In outbreak 2, R(0) was 18.89 (95%CI: 18.88-18.90) and VE was 98.54% (95%CI: 94.89-99.73). Consequently, P(c) was 112.97% (95%CI: 92.29-145.52) in outbreak 1 and 96.11% (95%CI: 93.81-98.53) in outbreak 2. CONCLUSION: Because of the lower VE in outbreak 1, measles virus transmission could not have been stopped even if all students received a single dose of vaccine. In outbreak 2, with higher VE, the outbreak could have been prevented by increasing the proportion of students who had been vaccinated.

Outbreak of Chlamydia pneumoniae infection in a Japanese nursing home, 1999-2000.

OBJECTIVE: To identify risk factors for infection and severe illness due to Chlamydia pneumoniae. METHODS: To identify risk factors for infection, we conducted a case-control study among nursing home residents who had onset of symptoms during December 1, 1999, to February 20, 2000. To identify risk factors for severe illness among nursing home residents, we conducted a retrospective cohort study. SETTING: A nursing home providing long-term and day care services for elderly patients in Japan.Participants. Fifty-nine residents and 41 staff members of a nursing home. RESULTS: The attack rates for respiratory illness were 53% (31 of 59) among residents and 22% (9 of 41) among staff. Infection was confirmed in 15 resident and 2 staff case patients by isolation of C. pneumoniae from nasal swab specimens. Fifteen resident case patients developed severe illness (ie, bronchitis, pneumonia, and hypoxia); one case patient died. The median age of resident case patients was 87 years. We could identify neither the source of the outbreak nor significant risk factors for infection and severe illness in residents. However, residents with a higher level of physical activity were more likely to become infected, whereas older residents (aged more than 85 years) and those with a lower level of physical activity were more likely to develop severe illness (P>.05). Contact with residents was a risk factor for infection in staff (relative risk, undefined; P=.04). CONCLUSIONS: C. pneumoniae can cause large outbreaks of infection and severe illness among elderly persons, and its transmission is likely to be enhanced by close contacts among people in nursing homes. Therefore, early detection of an outbreak by means of better surveillance, and subsequent isolation of patients, may be effective control measures.

[Compile and evaluation of national surveillance on human echinococcosis in Japan, 1999 to 2002].

National surveillance on human ecinococcosis has been performed since April 1999 when it was stipulated as a Category IV Disease under the Infectious Diseases Prevention Law. During the last 4 years of surveillance, 3 cases with unilocular hydatidosis (age range 27-81 years; median age 55 years) and 51 cases with alveolar hydatidosis (age range 15-86 years; median age 64 years) have been reported. The numbers of reported cases with alveolar hydatidosis have been increased with age, and the largest number reported in the age group > or = 71 years. Three cases with unilocular hydatidosis have been reported from health centers in Honshu, and were likely to be imported cases. Seventeen reported cases had clinical symptoms. None of the reported cases had information on infection route. Fifty out of 51 cases with alveolar hydatid disease have been reported from health centers in Hokkaido. When analyzing the cases by subdividing Hokkaido into six regional districts, large number of cases were reported from health centers in Ishikari-Shiribeshi-Iburi region (20 cases) and in Nemuro-Abashiri-Kushiro region (15 cases). As detailed addresses of the cases were masked, we compared the number of cases per 100,000 residents in regions. Health center in Nemuro-Abashiri-Kushiro region (2.13/100,000) had largest rate and second was Souya-Rumoi region (2.05/100,000). The results from current surveillance data only suggest the generation situation of human echinococcosis in several years ago or more, so the generation situation between 1999 April and 2002 December in surveillance is unknown.

Nosocomial Serratia marcescens outbreak in Osaka, Japan, from 1999 to 2000.

OBJECTIVES: To investigate and control an outbreak of bloodstream infections (BSIs) caused by Serratia marcescens and to identify risk factors for respiratory colonization or infection with S. marcescens. DESIGN: Epidemiologic investigation, including review of medical and laboratory records, procedural investigations, pulsed-field gel electrophoresis (PFGE) typing of environmental and patient isolates, statistical study, and recommendation of control measures. PATIENTS AND SETTING: All patients admitted to a 380-bed, secondary-care hospital in Osaka Prefecture, Japan, from July 1999 through June 2000 (study period). RESULTS: Seventy-one patients were colonized or infected with S. marcescens; 3 patients who developed primary BSIs on the same ward within 5 days in June 2000 had isolates with indistinguishable PFGE patterns and indwelling intravenous catheters for more than 5 days. On multivariate analysis, among 36 case-patients with positive sputum specimens and 95 control-patients, being bedridden (odds ratio [OR], 15.91; 95% confidence interval [CI95], 4.17-60.77), receiving mechanical ventilation (OR, 7.86; CI95, 2.27-27.16), being older than 80 years (OR, 3.12; CI95, 1.05-9.27), and receiving oral cleaning care (OR, 3.10; CI95, 1-9.58) were significant risk factors. S. marcescens was isolated from the fluid tanks of three nebulizers and a liquid soap dispenser. The hospital did not have written infection control standards, and many infection control practices were found to be inadequate (eg, respiratory equipment was used without disinfection between patients). CONCLUSIONS: Poor hospital hygiene and the lack of standard infection control measures contributed to infections hospital-wide. Recommendations to the hospital included adoption of written infection control policies.

A nosocomial outbreak of febrile bloodstream infection caused by heparinized-saline contaminated with Serratia marcescens, Tokyo, 2002.

In January 2002, 12 patients with Serratia marcescens bloodstream infection (BSI) were identified in a hospital in Tokyo, Japan. We conducted an epidemiological investigation of this outbreak. We undertook a medical-records review and employee interviews, and performed a case-control study to determine risk factors for S. marcescens BSI. An observational study of the hospital's procedures and an environmental microbiologic sampling were performed. We identified 12 suspected and 12 confirmed patients with S. marcescens BSI, including 7 who died. A case-control study showed that vascular access devices (odds ratio [OR] = 30.46; 95% confidence interval [CI] = 3.5-685.6) and the use of heparin-locks, between December 26 and January 15 (OR = 25.7; 95% CI = 2.3-680.4) were significant risk factors for S. marcescens BSI. The observational study revealed multiple lapses in infection control, including use of multi-dose vials of heparin. The outbreak strain was isolated from a hand-towel in the nurse station. The use of multi-dose vials of heparinized-saline during a particularly busy period was associated with BSI risk. The results underscore the risks inherent in infection-control lapses and the use of multi-dose vials.

Evaluation of a sentinel surveillance system for influenza, 1995-2000, Kyoto City, Japan.

We compared a municipal sentinel surveillance system for influenza with the Microbial Isolation Surveillance System (MISS) in Kyoto City, Japan. Sensitivity, specificity, and predictive value positive (PVP) of the Influenza Sentinel Surveillance System (ISSS) compared to the MISS were calculated by influenza season and by month. Sensitivity ranged from 80 to 97%, specificity ranged from 55 to 77%, and PVP ranged from 29 to 52% by season (P < 0.001). On the other hand, sensitivity ranged from 86 to 100%, specificity ranged from 38 to 66%, and PVP ranged from 31 to 50% by month (P < 0.001). Specificity was calculated as 93% in November. The sensitivity of ISSS was found to be sufficient regardless of the magnitude of influenza activity. Specificity varied by season, indicating the difficulty of clinically diagnosing other respiratory illnesses. The PVP remained at less than 50% before and after the influenza seasons and it varied year by year. In general, the ISSS is a good surveillance system for monitoring influenza activity.

Evaluation of National Tsutsugamushi Disease Surveillance--Japan, 2000.

In Japan, Tsutsugamushi disease, which is caused by Orientia tsutsugamushi, is re-emerging with newly recognized strains and is now endemic in all prefectures except Hokkaido and Okinawa. We analyzed recent surveillance data to describe the epidemiology of Tsutsugamushi disease and to evaluate the newly implemented national surveillance system according to the CDC guidelines for evaluating surveillance systems. In 2000, 756 cases of Tsutsugamushi disease were reported from 37 of 47 prefectures; two of these cases were fatal. The median age of case-patients was 64 years (range: 2 - 94 years); 414 (54.8%) were male. In northern Japan, most cases were diagnosed in the months of May through July and in the months of October through December, and in southern Japan, cases were diagnosed almost year-round with a peak from October through December and in January. Reporting and transfer of surveillance information from the prefecture to the national level was effective and timely, but the completeness and quality of case reporting could still be improved. The current system for Tsutsugamushi disease surveillance is useful for describing epidemiologic patterns by time, prefecture, and demographic characteristics. However, collection of additional information on suspected place of transmission, activity performed at the place of transmission, or the case-patient's profession would likely make the system more valuable for outbreak detection and for better defining populations at risk.

[Evaluation of national surveillance for echinococcosis in Japan, 1999 to 2002].

National echinococcosis surveillance has been performed since April 1999 when it was stipulated as a Category IV Disease under the Infectious Diseases Prevention Law. During the last 4 years of surveillance, 7 cases of unilocular hydatid disease (age range 27-81 years; median age 56 years) and 43 cases of alveolar hydatid disease (age range 24-83 years; median age 64 years) have been reported. There was an increase in the number of reported cases of alveolar hydatid with age, and the greatest number of reported cases occurred in the age group > or = 70 years. Thirty-three of the reported echinococcosis cases had clinical symptoms. The greatest number of echinococcosis was reported from health centers in Hokkaido; 94% of all reported cases (47/50) were from this island. After classifying Hokkaido into six regional districts and analyzing cases by district, we found the greatest number of reported cases to be from the Nemuro-Abashiri-Kushiro region (16 cases) and the Ishikari-Shiribeshi-Iburi region (15 cases). However, the greatest number of reported cases per 100,000 residents was found to be from the Souya-Rumoi region (2.05/100,000) and the Nemuro-Abashiri-Kushiro region (2.00/100,000). As the incubation period of echinococcosis is thought to be several years or more, the current data shows the infection rate from several years ago. In order to better understand the current infection rate of echinococcosis, we recommended implementing a seroepidemiological surveillance in addition to the present surveillance.

[Evaluation of public knowledge about influenza based on influenza hotline consultations].

In 1999, the Ministry of Health, Labour and Welfare issued guidelines on prevention and control of influenza. These included recommendations for public education about influenza and promotion of vaccination among persons at high risk for complications from influenza. In response, several public education programs were implemented, including an "influenza hotline" that was established within the Infectious Diseases Surveillance Center, National Institute of Infectious Diseases. To assess the informational needs of callers about influenza and evaluate the impact of different communication modalities, we analyzed data from telephone consultations made to the "influenza hotline" and from a survey that was conducted among a subset of callers. During the influenza seasons of 2000-2001 to 2002-2003, there was an average of 2,230 callers to the "influenza hotline" each season, range 1,809-2,696. The majority (42.4%) of callers were women aged 30-39 years, which might reflect young mothers. The most frequently asked questions were about influenza vaccination of infants and young children. which accounted for 20.6% (1,501/7,295) of all vaccine-related questions during the four seasons. Questions about the number of recommended influenza vaccine doses was the second most frequently asked topic and comprised 17.8% (1,300/7,295) of all vaccine-related questions. Over the period 2000-2001 to 2002-2003, questions about the recommended number of influenza vaccine doses decreased among elderly callers, but not for callers aged < 60 years. The number of calls about the location of influenza vaccine clinics, availability of influenza vaccine, and vaccination of elderly person declined from 1999-2000 to 2002-2003. Of callers that were surveyed (N = 3,316) about where they received information about influenza, the most frequently reported sources were newspapers (47.7%), and the internet (26.2%). Internet use by callers showed differences among age groups. Only 2.4% of callers aged > or = 60 years reported receiving influenza information through the internet in contrast to 33.9% among callers aged < 60 years. Our study suggests a high public demand for information about influenza, especially by mothers regarding influenza vaccination of infants and young children, and recommended influenza vaccine doses for adults. To improve education of the public about influenza, multiple communication strategies should be utilized, including written information, and the internet.

[Present status of Tsutsugamushi disease detection at regional public health laboratories--a comparison between the results from a questionnaire survey and the National Notifiable Diseases Surveillance System].

Tsutsugamushi disease has been a notifiable disease in Japan since the implementation of the Infectious Diseases Control Law in April 1999. In order to assess the role of public health laboratories in detecting Tsutsugamushi disease, a questionnaire regarding routine testing of suspected cases of Tsutsugamushi disease was sent to 73 regional public health laboratories (47 prefectural laboratories and 26 municipal laboratories) in July 2001. The response rate was 92% (67/73 laboratories). It was found that most prefectural laboratories are well prepared to routinely receive and test specimens of suspected Tsutsugamushi disease cases. Additionally, we found that some regional public health laboratories are using two or more detection methods to improve the accuracy of their routine tests. In southern Japan. Kawasaki and Kuroki strains, strains endemic to the region, are widely used in addition to Kato, Karp, and Gilliam strains, the standard strains used for serum antibody tests in Japan. For the years 2000 and 2001, we found that for some prefectures, the annual number of cases confirmed by regional public health laboratories was nearly equal to the annual number of cases the prefecture reported to the National Notifiable Diseases Surveillance System. In these prefectures, it appears that an effective communication network has been established between physicians, public health laboratories, and local health centers, ensuring laboratory confirmation and proper notification.

[An estimation of imported infections concerning 2002 FIFA world cup Korea/Japan].

The FIFA World Cup 2002 Korea/Japan, which will be held during May 31 through June 30, 2002, is a mass-gathering and high-profile event. The Ministry of Transport announced that approximately 430,000 people visit Japan for the event. We estimated the incidence of major imported infections using data from the national epidemiological surveillance of infectious diseases and the statistics of immigration. Estimated incidences are 5.88 (shigellosis), 3.41 (malaria), 1.40 (typhoid/paratyphoid fever), 0.42 (cholera), and 0.0032 (meningococcal meningitis). The incidence for viral hemorrhagic fever was estimated 0.0018 under assumption that "it correlates with the malaria incidence from Africa" and that "the incidence occurs every 15 years". These results indicate little possibility of remarkable increase of exotic infections during the event. These incidences, however, may occur in the rural prefectures where few cases are reported. It is highly needed to strengthen surveillance and educate physicians and public health experts especially for malaria cases.

[An evaluation of syndromic surveillance for the G8 Summit in Miyazaki and Fukuoka, 2000].

Syndromic surveillance was performed during the G8 Summit held in Fukuoka and Miyazaki City in July 2000. Any case suspected as acute infectious disease was reported from designated medical facilities. Those cases were categorized in 5 clusters including "hemorrhagic and skin symptoms", "respiratory symptoms", "gastroenteric symptoms", "neural symptoms", and "miscellaneous symptoms". To compare how closely these incidence trends were representing those of the infectious disease surveillance, these results were analyzed for two weeks. In Miyazaki, duplicated report were accepted when more than one symptom were found. The ratio of weekly reported number for each cluster was calculated for two weeks, and then the ratio for former/latter week was calculated for each cluster. The results from Fukuoka and Miyazaki surveillance revealed the average former/latter ratio +/- SD = 0.99 +/- 0.292, 95% CI; 0.71-1.28 and 1.19 +/- 0.298, 0.93-1.45, respectively. These results indicate that syndromic surveillance is well represented with the infectious disease surveillance trends. Single reporting, employed in Fukuoka, was easier for analysis. Reported number for acute respiratory syndrome was larger than that of infectious disease surveillance, indicating that the latter could not detect non-reportable adult cases. Syndromic surveillance enables us to show the trend quickly and it can be carried out with smaller costs and human resources. This study concluded that a syndromic surveillance is effective for such high-profile events, but sometimes it is hard to analyze the trend accurately, because of insufficient period of baseline data, number and size of the reporting sentinel facilities.

[Management of patients with viral hemorrhagic fever in Germany a comparison with the current Japanese system based on the who guidelines on emerging viral diseases].

OBJECTIVES: We investigated the German system for managing patients with viral hemorrhagic fever (VHF) in comparing with the current Japanese system. METHODS: In Germany, we visited the Robert Koch Institute and the isolation centers in Berlin and Leipzig. In Japan, we visited the isolation wards in the Narita Red Cross Hospital and the Rinku General Medical Center in Izumi-Sano, Osaka, to allow determination of differences in the systems. In terms of the "WHO program on emerging virus diseases, 1994", we then evaluated the two countries' systems. RESULTS: In Germany, the finding of a suspected case with VHF is promptly reported to the competent authorities at the local level. Public health physicians on 24-hour duty declare a quarantine alert and the case is transferred to one of five isolation centers not by plane but by ambulance car. The isolation rooms in Berlin, constructed some 20 years ago, are enclosed with plastic film and kept under negative pressure and this hinders it difficult to perform intensive care in the small space available. In contrast, intensive care and routine clinical tests can be readily conducted in the isolation facilities in Leipzig installed in 2000, since the rooms are spacious and kept under negative pressure. It is also noteworthy that the same ward is utilized for patients with drug-resistant infectious diseases to train medical staff. With 3 of the 4 goals in the WHO program, establishing efficient surveillance of infectious diseases, provision of a qualified national laboratory and performance on practical research on infectious diseases, there are no large differences, between the two countries, in continuous efforts in line with recently-modified infectious disease laws. However, we found differences with regard to an effective strategy to circumvent VHF, 1) local government has a main role against VHF and control team is promptly designated in Germany, 2) only 10 beds are equipped to deal with VHF in Germany, 3) management of air-droplet infection seems insufficient in Japan, 4) highly-equipped isolation rooms are not utilized for patients other than those with VHF in Japan. CONCLUSIONS: These findings require urgent discussion among Japanese experts concerning; 1) operation of BSL4 facilities in national laboratories; 2) collaboration among quarantine stations, local government and national reference laboratories; 3) the appropriate number of isolation wards; 4) practical procedures to run of isolation wards efficiently; 5) the possibility of utilizing isolation wards for non-VHF.

Seroprevalence of antibodies to pandemic (H1N1) 2009 influenza virus among health care workers in two general hospitals after first outbreak in Kobe, Japan.

OBJECTIVE: To assess the prevalence including asymptomatic infection, infection risk of exposure to patients, and effectiveness of personal protective equipment (PPE) among health care workers (HCWs) during the first pandemic (H1N1) 2009 (pH1N1) outbreak in Kobe, Japan in May 2009. METHODS: A cross-sectional seroepidemiological study was conducted on 268 HCWs in the two hospitals in Kobe to which all pH1N1 inpatients were directed. Participating HCWs completed a self-administrated questionnaire and provided a single serum sample which was analyzed using a hemagglutination-inhibition (HI) antibody test. RESULTS: Of 268 subjects, 14 (5.2%) were found to have positive antibodies to the pH1N1 by HI assay; only 1 reported a febrile episode. Among the 14 seropositive cases, 8 received chemoprophylaxis. 162 HCWs (60.4%) had been exposed to patients. The seropositive rate (SPR) for pH1N1 of the exposed group was higher than that of the unexposed group, however not statistically significant (6.8% vs. 3.1%, p = 0.197). There were no statistically significant differences in SPR for any PPE. CONCLUSION: The SPR for pH1N1 in the exposed group was higher than that of the unexposed group in HCWs; however, most of these individuals were asymptomatic. There was no statistically significant association between PPE implementation and pH1N1 seropositivity.