Influenza in travellers:

Epidemiology and genomic characterisation of travel-associated and locally-acquired influenza, Marseille, France

BACKGROUND

The purpose of the study was to challenge the hypothesis of an introduction of influenza viruses by international travellers and subsequent local circulation in Marseille, France.

METHODS

We analysed the epidemiological data of PCR-confirmed cases over an eight-year period and compared the genomic data of local and imported influenza viruses during a six-month period.

RESULTS

Between June 2013 and December 2020, 12,434 patients in the Assistance Publique-Hospitaux de Marseille were diagnosed with an influenza virus infection at the laboratory of the Institut Hospitalo-Universitaire Méditerranéee Infection of Marseille. Half of the patients were below the age of 20. Most of the imported cases were diagnosed outside of epidemic periods. Fourteen genomes of the influenza A virus, including six in international travellers returning from Europe or from the Arabian Peninsula and eight from patients who had not travelled were analysed. Sequences of influenza A/H1N1 virus genomes detected in subjects who had travelled to Saudi Arabia were in the same clade and differed from sequences detected later in a traveller returning from Italy, and in non-travellers who were infected in Marseille. This suggests that influenza viruses imported from Saudi Arabia did not subsequently circulate in Marseille.

CONCLUSION

Future studies with higher numbers of genomes are needed to confirm this result.

Influenza-Like Illness in Travelers to the Developing World

Travelers to developing regions are at risk for development of influenza-like illness (ILI). Little is known of traveler and trip characteristics associated with the development of ILI. TravMil is a prospective observational study, enrolling subjects presenting to six military travel clinics or predeployment-screening sites. We analyzed pre- and post-travel surveys from travelers visiting regions outside of the continental United States, Western or Northern Europe, Canada, Australia, or New Zealand between January 2010 and March 2016. Influenza-like illness was defined as a self-reported fever associated with either sore throat or cough. Trip and traveler characteristics were analyzed to determine risk factors for the development of ILI. Two thousand nine hundred and thirty-two trips were recorded (55% male, median age 45 years, 69% white, 51% on vacation, median travel duration 17 days). The 2,337 trips included the number of self-reported influenza vaccinations in the preceding 5 years (median 5). Eleven percent of the trips were complicated by an ILI lasting a median of 5 days; 70% and 17% of these reported upper and lower respiratory tract infection, respectively, and 12% reported both. On multivariate analysis, increased risk of ILI was associated with female gender (odds ratio [OR]: 1.60 [confidence interval (CI): 1.25-2.05], P < 0.01), age (years) (OR: 1.01 [CI: 1.01-1.02], P < 0.01); and duration of travel (days) (OR: 1.01 [CI: 1.00-1.01], P < 0.01). Influenza-like illness is common in travelers, regardless of traveler characteristics, purpose of travel, destination, or season of year. Female gender, older age, and longer duration of travel were associated with an increased risk of ILI. Additional tools and strategies are needed to prevent ILI in international travelers.

Detection of influenza A(H1N1)pdm09 virus in a patient travelling from Shanghai to Italy in July 2018: an uncommon clinical presentation in a non-seasonal period

Influenza is one of the most common infectious diseases in travellers, especially in those returning from subtropical and tropical regions.

In late June 2018 an influenza A(H1N1)pdm09 virus infection was diagnosed in a 36-years-old man, returned from a travel in Shanghai and hospitalized at the Ospedale Policlinico San Martino, Genoa, Italy, with a diagnosis of fever and an uncommon clinical presentation characterised by a persistent leukopenia. Phylogenetic analysis revealed a closeness with influenza A(H1N1)pdm09 strains circulating in the US in May-June 2018.

Prompt recognition of influenza infection led to a proper case management, demonstrating the crucial role of the continuous influenza surveillance programme.

Spatiotemporal diffusion of influenza A (H1N1): Starting point and risk factors

Influenza constitutes a major challenge to world health authorities due to high transmissibility and the capacity to generate large epidemics. This study aimed to characterize the diffusion process of influenza A (H1N1) by identifying the starting point of the epidemic as well as climatic and sociodemographic factors associated with the occurrence and intensity of transmission of the disease. The study was carried out in the Brazilian state of Paraná, where H1N1 caused the largest impact. The units of spatial and temporal analysis were the municipality of residence of the cases and the epidemiological weeks of the year 2009, respectively. Under the Bayesian paradigm, parametric inference was performed through a two-part spatiotemporal model and the integrated nested Laplace approximation (INLA) algorithm. We identified the most likely starting points through the effective distance measure based on mobility networks. The proposed estimation methodology allowed for rapid and efficient implementation of the spatiotemporal model, and provided evidence of different patterns for chance of occurrence and risk of influenza throughout the epidemiological weeks. The results indicate the capital city of Curitiba as the probable starting point, and showed that the interventions that focus on municipalities with greater migration and density of people, especially those with higher Human Development Indexes (HDIs) and the presence of municipal air and road transport, could play an important role in mitigation of effects of future influenza pandemics on public health. These results provide important information on the process of introduction and spread of influenza, and could contribute to the identification of priority areas for surveillance as well as establishment of strategic measures for disease prevention and control. The proposed model also allows identification of epidemiological weeks with high chance of influenza occurrence, which can be used as a reference criterion for creating an immunization campaign schedule.

Mismatching between circulating strains and vaccine strains of influenza: Effect on Hajj pilgrims from both hemispheres

The trivalent seasonal influenza vaccine is expected to provide optimum protection if the vaccine strains match the circulating strains. The effect of worldwide mismatch between the vaccine strains and extant strains on travelers attending Hajj pilgrimage is not known. Annually 2-3 million Muslims coming from north and south hemispheres congregate at Hajj in Mecca, Saudi Arabia, where intense congestion amplifies the risk of respiratory infection up to eight fold. In order to estimate, to what extent mismatching increases the risk of vaccine failure in Hajj pilgrims, we have examined the global data on influenza epidemiology since 2003, in light of the available data from Hajj. These data demonstrate that globally mismatching between circulating and vaccine strains has occurred frequently over the last 12 years, and the mismatch seems to have affected the Hajj pilgrims, however, influenza virus characteristics were studied only in a limited number of Hajj seasons. When the vaccines are different, dual vaccination of travelers by vaccines for southern and northern hemispheres should be considered for Hajj pilgrims whenever logistically feasible. Consideration should also be given to the use of vaccines with broader coverage, i.e., quadrivalent, or higher immunogenicity. Continuous surveillance of influenza at Hajj is important.

Ability of physicians to diagnose influenza and usefulness of a rapid influenza antigen test in febrile returning travelers: A randomized controlled trial

BACKGROUND

Fever is a frequent cause of medical consultation among returning travelers. The objectives of this study were to assess whether physicians were able to identify patients with influenza and whether the use of an influenza rapid diagnostic test (iRDT) modified the clinical management of such patients.

METHODS

Randomized controlled trial conducted at 2 different Swiss hospitals between December 2008 and November 2012. Inclusion criteria were 1) age ≥ 18 years, 2) documented fever of ≥ 38 °C or anamnestic fever + cough or sore throat within the last 4 days, 3) illness occurring within 14 days after returning from a trip abroad, 4) no definitive alternative diagnosis. Physicians were asked to estimate the likelihood of influenza on clinical grounds, and a single nasopharyngeal swab was taken. Thereafter patients were randomized into 2 groups: i) patients with iRDT (BD Directigen A + B) performed on the nasopharyngeal swab, ii) patients receiving usual care. A quantitative PCR to detect influenza was done on all nasopharyngeal swabs after the recruitment period. Clinical management was evaluated on the basis of cost of medical care, number of X-rays requested and prescription of anti-infective drugs.

RESULTS

100 eligible patients were referred to the investigators. 93 patients had a naso-pharyngeal swab for a PCR and 28 (30%) swabs were positive for influenza. The median probability of influenza estimated by the physician was 70% for the PCR positive cases and 30% for the PCR negative cases (p < 0.001). The sensitivity of the iRDT was only 20%, and specificity 100%. Mean medical cost for the patients managed with iRDT and without iRDT were USD 581 (95%CI 454-707) and USD 661 (95%CI 522-800) respectively. 14/60 (23%) of the patients managed with iRDT were prescribed antibiotics versus 13/33 (39%) in the control group (p = 0.15). No patient received antiviral treatment.

CONCLUSION

Influenza was a frequent cause of fever among these febrile returning travelers. Based on their clinical assessment, physicians had a higher level of suspicion for influenza in PCR positive cases. The iRDT used in this study showed a disappointingly low sensitivity and can therefore not be recommended for the management of these patients.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00821626.

Changes in the prevalence of influenza-like illness and influenza vaccine uptake among Hajj pilgrims: A 10-year retrospective analysis of data

BACKGROUND

Influenza is an important health hazard among Hajj pilgrims. For the last ten years, pilgrims are being recommended to take influenza vaccine before attending Hajj. Vaccination coverage has increased in recent years, but whether there has been any change in the prevalence of influenza-like illness (ILI) is not known. In this analysis, we examined the changes in the rate of ILI against seasonal influenza vaccine uptake among Hajj pilgrims over the last decade.

METHOD

Data for this analysis is a synthesis of raw and published data from eleven Hajj seasons between 2005 and 214. For seven Hajj seasons the data were obtained from studies involving pilgrims of UK, Saudi Arabia and Australia; and for the remaining four Hajj seasons data were abstracted from published studies involving pilgrims from multiple countries. The data from both sources were synthesised to estimate the relative risk (RR) of acquisition of ILI in vaccinated versus unvaccinated pilgrims.

RESULTS

The pooled sample size of the included studies was 33,213 with most pilgrims being in the age band of 40-60 years (range: 0.5 to 95 years) and a male to female ratio of 1.6. The pilgrims originated, in order of frequency, from Iran, Australia, France, UK, Saudi Arabia, Indonesia, India, Algeria, Ivory Coast, Nigeria, Somalia, Turkey, Syria, Sierra Leone and USA. Except for one year (2008), data from individual years did not demonstrate a noticeable change in the rate of ILI against influenza vaccine coverage, however the combined data from all studies suggest that the prevalence of ILI decreased among Hajj pilgrims as the vaccine coverage increased over the last decade (RR 0.2, P<0.01).

CONCLUSION

This analysis suggests that influenza vaccine might be beneficial for Hajj pilgrims. However, controlled trials aided by molecular diagnostic tools could confirm whether such an effect is real or ostensible.

Viral respiratory infections among Hajj pilgrims in 2013

Middle East respiratory syndrome coronavirus (MERS-CoV) has emerged in the Arabian Gulf region, with its epicentre in Saudi Arabia, the host of the 'Hajj' which is the world's the largest mass gathering. Transmission of MERS-CoV at such an event could lead to its rapid worldwide dissemination. Therefore, we studied the frequency of viruses causing influenza-like illnesses (ILI) among participants in a randomised controlled trial at the Hajj 2013. We recruited 1038 pilgrims from Saudi Arabia, Australia and Qatar during the first day of Hajj and followed them closely for four days. A nasal swab was collected from each pilgrim who developed ILI. Respiratory viruses were detected using multiplex RT-PCR. ILI occurred in 112/1038 (11%) pilgrims. Their mean age was 35 years, 49 (44%) were male and 35 (31%) had received the influenza vaccine pre-Hajj. Forty two (38%) pilgrims had laboratory-confirmed viral infections; 28 (25%) rhinovirus, 5 (4%) influenza A, 2 (2%) adenovirus, 2 (2%) human coronavirus OC43/229E, 2 (2%) parainfluenza virus 3, 1 (1%) parainfluenza virus 1, and 2 (2%) dual infections. No MERS-CoV was detected in any sample. Rhinovirus was the commonest cause of ILI among Hajj pilgrims in 2013. Infection control and appropriate vaccination are necessary to prevent transmission of respiratory viruses at Hajj and other mass gatherings.

Effect of travel on influenza epidemiology

To assess the attack and incidence rates for influenza virus infections, during October 2006–October 2007 we prospectively studied 1,190 adult short-term travelers from the Netherlands to tropical and subtropical countries. Participants donated blood samples before and after travel and kept a travel diary. The samples were serologically tested for the epidemic strains during the study period. The attack rate for all infections was 7% (86 travelers) and for influenza-like illness (ILI), 0.8%. The incidence rate for all infections was 8.9 per 100 person-months and for ILI, 0.9%. Risk factors for infection were birth in a non-Western country, age 55–64 years, and ILI. In 15 travelers with fever or ILI, influenza virus infection was serologically confirmed; 7 of these travelers were considered contagious or incubating the infection while traveling home. Given the large number of travelers to (sub)tropical countries, travel-related infection most likely contributes to importation and further influenza spread worldwide.

Prevention of influenza among travellers attending at a UK travel clinic: beliefs and perceptions. A cross-sectional study

BACKGROUND

Travellers' compliance with measures to prevent influenza through the use of antivirals and influenza vaccine remains very poor despite influenza being one of the commonest travel and vaccine-preventable diseases. A study was undertaken to assess travellers' beliefs, perceptions and intentions to take antivirals for the treatment and prevention of influenza during the H1N1 pandemic.

METHODS

A cross-sectional survey (n = 96) of travellers who attended the Royal Free Travel Health Centre, London, UK was undertaken in September 2009. A self-administered questionnaire was completed by a traveller in advance of their pre-travel health consultation. Logistic regression identified variables independently associated with compliance.

RESULTS

Influenza vaccination uptake for the 5 years preceding the study was found to be 20·8%. This was statistically significantly higher for older travellers and those with underlying health conditions (P < 0·005). Mean intention to comply with antiviral drugs on a preventive and therapeutic basis was 58% and 72%, respectively, and this varied markedly with age and with dispensed antimalarial chemoprophylaxis.

CONCLUSION

This study identifies some beliefs and perceptions travellers consider with regard to the therapeutic and preventive influenza use of antivirals during the H1N1 pandemic; it underscores the importance of travellers receiving hemisphere appropriate influenza vaccination. The external validity of these study findings requires further corroboration involving other travel clinics and different cohorts of travellers during seasonal activity or outbreaks of influenza. These findings could guide the development of future strategies for the prevention of influenza in travellers.

The burden of influenza B: a structured literature review

We reviewed the epidemiology, clinical characteristics, disease severity, and economic burden of influenza B as reported in the peer-reviewed published literature. We used MEDLINE to perform a systematic literature review of peer-reviewed, English-language literature published between 1995 and 2010. Widely variable frequency data were reported. Clinical presentation of influenza B was similar to that of influenza A, although we observed conflicting reports. Influenza B-specific data on hospitalization rates, length of stay, and economic outcomes were limited but demonstrated that the burden of influenza B can be significant. The medical literature demonstrates that influenza B can pose a significant burden to the global population. The comprehensiveness and quality of reporting on influenza B, however, could be substantially improved. Few articles described complications. Additional data regarding the incidence, clinical burden, and economic impact of influenza B would augment our understanding of the disease and assist in vaccine development.

Latitudinal patterns of travel among returned travelers with influenza: results from the GeoSentinel Surveillance Network, 1997-2007

BACKGROUND

Influenza is a common vaccine-preventable disease among international travelers, but few data exist to guide use of reciprocal hemisphere or out-of-season vaccines.

METHODS

We analyzed records of ill-returned travelers in the GeoSentinel Surveillance Network to determine latitudinal travel patterns in those who acquired influenza abroad.

RESULTS

Among 37,542 ill-returned travelers analyzed, 59 were diagnosed with influenza A and 11 with influenza B. Half of travelers from temperate regions to the tropics departed outside influenza season. Twelve travelers crossed hemispheres from one temperate region to another, five during influenza season. Ten of 12 travelers (83%) with influenza who crossed hemispheres were managed as inpatients. Proportionate morbidity estimates for influenza A acquisition were highest for travel to the East-Southeast Asian influenza circulation network with 6.13 (95% CI 4.5-8.2) cases per 1000 ill-returned travelers, a sevenfold increased proportionate morbidity compared to travel outside the network.

CONCLUSIONS

Alternate hemisphere and out-of-season influenza vaccine availability may benefit a small proportion of travelers. Proportionate morbidity estimates by region of travel can inform pre-travel consultation and emphasize the ease of acquisition of infections such as influenza during travel.

Travel health: routine, recommended and required vaccines

Vaccines are an important public health measure and may be the prompt for travellers to attend for pre-travel health advice. Nurses involved in the provision of travel health advice require a sound knowledge of available vaccines together with the diseases they prevent and other risk management strategies. Travel vaccines should always be administered following a travel health consultation and risk assessment, taking into account the informed choice of the traveller. This paper discusses vaccine preventable disease in the context of travel health, and the appropriate use of routine, recommended and required pre-travel vaccines, which can be considered following individual risk assessment.