Annelies Wilder-Smith, MD, PhD, FAMS, Head, Travellers’ Health and Vaccination Centre, Department of Infectious Diseases, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore 308433. Email: firstname.lastname@example.org
Introduction Pertussis is a worldwide, highly communicable, vaccine-preventable respiratory disease and is a frequent but often underestimated cause of prolonged cough illness in adults. Immunity from childhood pertussis immunization is thought to last only up to 10 years. The incidence of adult pertussis has been estimated to be 200 to 500 per 100,000 persons-years. Acellular pertussis vaccines have been evaluated in adults and confer safe and effective protection and now exist as combination vaccine together with tetanus and diphtheria.
Methods We did a questionnaire survey to assess the knowledge, attitude, and practices toward pertussis in adult travelers. We consecutively enrolled all travelers who presented at the Travellers’ Health & Vaccination Centre in Singapore in 1 month.
Results Of 218 consecutively enrolled travelers, 184 (84.4%) completed the questionnaire; of which 80% were Singaporeans. Seventy persons (38%) did not know or gave a wrong answer for the mode of transmission of pertussis, 147 (83%) had never heard of a pertussis vaccine for adults, and almost none had received an adult pertussis vaccine booster. Travelers from Western countries were seven times [95% confidence interval (CI): 2—27] more likely than Asians to have knowledge about pertussis; women were 4.27 times (95% CI: 1.59–11.53) more likely than men to be aware of the booster vaccine, after adjusting for nationality ( p= 0.004).
Conclusions Knowledge about pertussis was poor among adult travelers. Although pertussis was viewed as a serious illness by the majority of participants, and 38% expressed the desire to be vaccinated, almost no one had received the pertussis vaccine booster. Awareness about pertussis, its risks, and prevention via vaccination need to be increased among adult travelers. Studies are needed to quantify the risk of pertussis in adult travelers.
Pertussis is a highly communicable, vaccine-preventable respiratory disease and is a frequent but often underestimated cause of prolonged cough illness in adults.1 Whereas in children pertussis is characterized by paroxysmal cough, whooping cough, and posttussive vomiting, in adults the disease is often atypical, sometimes manifested only by a protracted nondistinctive cough.2 High attack rates of pertussis have been observed among adults in the setting of community outbreaks of pertussis, even in highly immunized populations, and this is thought to reflect waning of the immunity from childhood vaccination.3 About a quarter of prolonged cough illnesses in adults is due to pertussis.1,2,4 The incidence of adult pertussis has been estimated to be 200 to 500 per 100,000 persons-years.5–8 Adults are often also the source of infection for young children.9 The morbidity in adults is mainly associated with prolonged cough, with the average duration being 44 days.1 Complications increase with age.1 Rare complications are hemoptysis, otitis media, pneumonia, urinary incontinence, rib fractures, pneumothorax, cough syncope, seizures, and loss of consciousness triggered by coughing episodes.10 The economic burden of pertussis in adults is substantial, and therefore, broader use of adult booster vaccination would be justified.6,11 Furthermore, adolescents and adults are a major source of infection in young infants.9 This puts those below the age of 6 months at particular risk as they are not yet protected by childhood immunization against pertussis.
Pertussis vaccines have been in routine pediatric use for more than 50 years and have dramatically decreased the incidence and complications of whooping cough in children,12,13 but protection is thought to be minimal after 10 years without boosting.14,15 Because of concerns about the reactogenicity of whole-cell pertussis vaccines in older children and adults, no booster vaccinations were recommended. Acellular pertussis vaccines have now been evaluated in adolescents and adults and confer safe and effective protection against pertussis,14 also as combination vaccine together with tetanus and diphtheria (Tdap).16,17 In a large prospective study in the United States using the tricomponent acellular pertussis vaccine, the vaccine protection was 92%.8 As adult travelers often require a booster for tetanus and diphtheria prior to their travel, this is an opportunity to offer the combined vaccine for adult tetanus, diphtheria, and acellular pertussis. However, no data are available that identify the travelers’ awareness of pertussis, their perceived risk of pertussis, and their attitude toward receiving an adult pertussis vaccine booster.
We did a questionnaire survey on knowledge, attitude, and practices toward adult pertussis booster. We consecutively enrolled all travelers who presented at the Travellers’ Health & Vaccination Centre in Singapore in January 2006. The self-administered questionnaire contained 18 questions related to demographics, knowledge, attitude, and practices toward pertussis, tetanus, and diphtheria and their respective vaccines and included a brief explanation that pertussis equals whooping cough. We excluded subjects who did not respond to the questionnaire or who completed less than 50%.
We grouped professional background into professionals and nonprofessionals and classified nationalities into Asian, Western travelers, and others. Asian travelers were defined as those with a nationality from South, East, and Southeast Asia, excluding the Middle East. Western travelers were defined as those with a nationality from the United States, Canada, Europe, Australia, or New Zealand.
Data analysis was carried out in Stata V9.0 (Stata Corp., College Station, TX, USA), and all statistical tests were conducted at the 5% level of significance.
Logistic regression models were used to identify factors associated with perceived risk of pertussis, perceived knowledge of pertussis booster vaccine, and willingness to receive the combined tetanus/diphtheria/acellular pertussis vaccine over the tetanus/diphtheria vaccine. Starting from the most significant factor identified in the univariate analysis, we used the likelihood ratio test to determine if inclusion of a covariate helped improve the fit of the model. For variables that were continuous in the measurement scale, we tested for nonlinearity by including a quadratic term in the model and testing for its significance. Odds ratios and their corresponding 95% confidence intervals (CI) were computed as estimates of the effect size.
The study was approved by the Ethics Committee, Tan Tock Seng Hospital, Singapore.
In total, 218 travelers were eligible for enrollment; of these, 184 completed the survey (response rate 84%). Table 1 summarizes the demographic characteristics of the 184 survey participants.
Table 1. Demographic composition of study respondents (N= 184)
Numbers and percentages may not add up to 184 (100%) due to nonresponse.
Diploma/degree and above
High school (O/A level)
Secondary and below
35 years (range 14–70 y)
Prolonged cough (more than 2 wk) within the past 1 y
Ever been hospitalized for lung infections
Seventy persons (38%) did not know or gave a wrong answer for the mode of transmission of pertussis. Table 2 depicts the knowledge of mode of transmission in comparison to tetanus and diphtheria. The level of knowledge about the mode of transmission for pertussis was similar to that for tetanus (62 vs 61%). On multivariate analysis, knowledge on mode of transmission for pertussis was independent of gender, nationality, age, education, and professional background. Thirty participants (17%) had heard of a combined adult tetanus/diphtheria/pertussis booster, while 115 (62%) had heard of an adult tetanus booster. As for the predictors of knowledge of pertussis booster vaccine, we found that nationality and gender were independently associated with knowledge (Table 3). Westerners were seven times (95% CI: 2–27) more likely than Asians to have this knowledge, after adjusting for sex, and this was found to be statistically significant (p= 0.002). Women were 4.27 times (95% CI: 1.59–11.53) more likely than men to be aware of the booster vaccine, after adjusting for nationality ( p= 0.004). For those travelers with children (n= 118), Western travelers were significantly more likely to know that their children were vaccinated against pertussis compared to Asians; the odds ratio was 20 (95% CI: 4.41–96.94), p < 0.001. The knowledge about an adult pertussis vaccine booster was much lower compared to the adult tetanus vaccine booster: 30 (16%) were aware that an adult pertussis vaccine existed versus 115 (62%) for the adult tetanus booster. Westerners were four times more likely to know about the adult tetanus vaccine booster compared to Asian travelers, although this was not found to be significant (p= 0.055).
Table 2. Knowledge about mode of transmission
Coughing or sneezing of droplets
Food and water
Diphtheria, n (%)
Tetanus, n (%)
Pertussis, n (%)
Table 3. Predictors of knowledge on the existence of pertussis booster vaccine and predictors of willingness to be vaccinated with the combined pertussis/diphtheria/tetanus vaccine (Dtap)
Predictors of knowledge on the existence of a pertussis booster vaccine
Predictors of willingness to receive the combined pertussis vaccine
CI = confidence interval; OR = odds ratio.
A levels and below
Diploma/degree and above
Age (every year increase)
Pertussis was viewed as a life-threatening disease by 52% of the participants, while tetanus was viewed as potentially life-threatening by 75%, diphtheria by 61%, severe acute respiratory syndrome (SARS) by 98%, and common cold by 6% (Table 4). Pertussis vaccination was considered to be important or essential by 46% compared to 54 and 52% for tetanus and diphtheria vaccine booster, respectively.
Table 4. Perception of seriousness of infectious diseases in adults
A mild disease
Causes illness but not dangerous
May be life threatening
“Common cold”, n (%)
SARS, n (%)
Influenza (“flu”), n (%)
Diphtheria, n (%)
Pertussis, n (%)
Tetanus, n (%)
Five (3%) had received a combined tetanus/diphtheria/pertussis booster in the past 10 years, in contrast to 55 (33%) who had received a tetanus booster in the past 10 years. Sixty persons (38%) were willing to pay an additional amount for the combined tetanus/diphtheria/pertussis vaccine over the tetanus/diphtheria vaccine. Gender was the only independent factor associated with willingness to pay an additional amount for the combined pertussis vaccine, with men being less likely compared to women to pay more to receive the booster, with an odds ratio of 0.4 (95% CI: 0.2–0.8, p= 0.007). Figure 1 shows the proportion of travelers who considered pertussis as a major threat, but have not received the adult pertussis vaccine booster, although a substantial proportion was willing to receive an adult pertussis booster.
This survey demonstrates that knowledge about adult pertussis booster vaccine was very poor among adult travelers and far less compared to the adult tetanus booster vaccine. On multivariate analysis, poor knowledge was independent of the educational level, professional background, and nationality, indicating a general lack of knowledge. Public awareness about pertussis, therefore, appears to be a problem. Lack of knowledge about adult pertussis has even been described in physicians and family medicine practitioners,18 and this is likely to be a major contributing factor to the lack of knowledge in the public.
Western travelers were significantly more likely to know about an adult pertussis vaccine compared to Asian travelers. This difference in knowledge was particularly profound when it came to knowledge about childhood pertussis vaccination (odds ratio was 20). Previous studies have shown that knowledge about vaccine-preventable diseases in Asian travelers lacks behind that of Western travelers.19 International travel among Asians is rapidly expanding, while uptake on pretravel health advice and travel vaccinations remains poor.19 There is an urgent need for enhanced public education on travel vaccines among Asian travelers.
The survey highlighted an interesting observation that 52% of adult travelers perceive pertussis as a life-threatening disease and a similar proportion consider pertussis vaccination as important. Despite this attitude, only 17% had heard of an adult pertussis vaccine and almost no one had received a pertussis vaccine in the past 10 years. The adult acellular pertussis vaccine and Tdap (=adult/adolescent booster with tetanus, diphtheria, and acellular pertussis) are relatively new and not yet registered in all countries. Lack of access to this vaccine is, therefore, a likely explanation for the low uptake of this vaccine in this cohort. In Singapore, for example, Tdap was introduced only in 2003. Furthermore, in this study we did not validate the responses by comparison with actual vaccine records. The study results should, therefore, be interpreted in light of potential recall problems.
Universal adult booster vaccination against pertussis remains controversial.20 Pertussis vaccination for adult travelers is not standard practice, although the latest recommendations of the Advisory Committee on Immunization Practices recommends that all adolescents aged 11 to 18 years should receive a single dose of Tdap instead of the adolescent/adult booster tetanus and diphtheria toxoids vaccine (Td) if they have completed the recommended childhood diphtheria, tetanus, and pertussis vaccination series.21 The recommendations from the International Consensus Group on Pertussis Immunisation state that public health policy makers should target pertussis booster to adult risk groups.14 Several countries have already introduced Tdap for high-risk groups such as health care workers.18 Data on incidence of pertussis in general adult travelers are lacking, and therefore, it remains unknown whether travelers belong to the high-risk group. One study found a high incidence of pertussis in a particular subpopulation of travelers, namely, the hajj pilgrims.22 The overall incidence rate of pertussis (1.4%) during this 1-month-long pilgrimage22 was found to be higher than that of most other vaccine-preventable travel-related diseases (except influenza)23 and higher than that reported in other risk groups such as health care workers.5 Hajj pilgrims would, therefore, benefit from a pertussis vaccination prior to their departure. However, the high incidence of pertussis in hajj pilgrims cannot be extrapolated to general travelers, as epidemiological factors that lead to enhanced transmission of pertussis, such as overcrowding, differ between the hajj pilgrimage and general tourist travel. Carefully designed studies to determine the incidence of pertussis in general travelers are now needed to evaluate whether general travelers should be targeted for adult pertussis booster. Given the fact that pertussis is a worldwide problem,18 pertussis is likely to be a risk to general travelers, compounded by the fact that national immunization programs against pertussis in some tropical destination countries may be suboptimal. Respiratory problems are the most common complaint in returning travelers as shown in a large cohort of more than 18,000 international travelers.24 Travelers often encounter situations of overcrowding such as in airplanes, buses, trains, markets, festivals, and so on.
Although knowledge about pertussis was poor, a substantial proportion of participants in this survey were keen to receive the combined tetanus/diphtheria/acellular pertussis vaccine over the traditional tetanus or tetanus/diphtheria booster, as reflected by their willingness to pay an additional amount of money. Western travelers were significantly more willing to do so, indicating again an increased awareness about adult vaccinations in Western travelers compared to Asian travelers. Female travelers were also significantly more willing to receive an adult pertussis vaccine compared to male travelers. This is likely a reflection of the different health-seeking behavior in women.
In summary, this study demonstrates the need for enhanced public awareness on pertussis and adult/adolescent pertussis booster vaccine in travelers. Prospective studies on the incidence of pertussis in general travelers are necessary to quantify the specific risk related to travel.
A. W.-S., I. B., and H. L. B. had the study idea. A. W.-S. and I. B. designed the survey questionnaire. A. W.-S. and S. L. H. conducted the survey, and A. E. and A. W.-S did the statistical analysis and data interpretation. A. W.-S wrote the paper, and all other authors contributed to the final manuscript.
Declaration of Interests
GlaxoSmithKline sponsored the study. A. W.-S. did not receive any investigator fees for this study. However, she has received reimbursements to attend conferences and speaker’s fees by GlaxoSmithKline and Sanofi Pasteur. I. B. is working for GlaxoSmithKline as director, clinical R&D, and medical affairs, Australasia. A. E. received a fee to conduct the statistical analysis from GlaxoSmithKline. S. L. H. states no conflicts of interest. H. B. is working for GlaxoSmithKline Biologicals as vice president/director, clinical R&D, and medical affairs in charge of Asian Pacific, Australasia, China/Hong Kong, and Japan.