Globally, nearly 600 million people fall ill each year due to contaminated food, resulting in 420,000 deaths (1). One of the most common foodborne pathogens is Staphylococcus aureus, which produces 21 known enterotoxins and exhibits increasing resistance to antibiotics (2, 3). In about 30 % of the human population who are persistent carriers, nostrils act as the primary reservoir, and hands as the main vector for transmission, although airborne dissemination may also contribute to disease outbreaks (4).
Food contamination with S. aureus can lead to staphylococcal food poisoning, especially in vulnerable groups, characterised by nausea, vomiting, and abdominal cramps, which typically develop within 30 min to 8 h and resolve within 24–48 h (5, 6). Most often, food contamination occurs in dairy products, cereals, processed meats, and ready-to-eat meals (7, 8), which points to food handlers, nasal carriers in particular, as the most likely source (9, 10).
However, information about nasal carriage of S. aureus among workers involved in food production, distribution, and trade in the Republic of North Macedonia is scarce, even though they undergo monitoring every six months. The aim of our study was therefore to address this gap and to investigate the relationship between nasal carriage of S. aureus and personal hygiene practices in this population.
This cross-sectional study was conducted at the Institute of Public Health in Skopje, North Macedonia, between November 2021 and March 2022 as part of mandatory health and hygiene examinations of workers employed in food production, distribution, and trade. It included 289 participants (140 men and 149 women) who voluntarily agreed to participate, completed the questionnaire, and gave written informed consent prior to inclusion in the study.
Data collection included microbiological testing and a structured questionnaire. A single nasal swab was obtained from each participant and immediately inoculated onto blood agar plates. Plates were incubated at 35–37 °C for 24 h. Presumptive staphylococcal colonies were identified based on colony morphology and Gram staining, which demonstrated Gram-positive cocci arranged in grape-like clusters. Catalase testing was performed to confirm the genus Staphylococcus, while S. aureus was differentiated from coagulase-negative staphylococci (CoNS) using the DNase test.
Methicillin resistance was determined phenotypically using the cefoxitin (30 µg) disc diffusion method on Mueller-Hinton agar. Inhibition zone diameters were measured and interpreted according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines (11). Isolates with inhibition zones <22 mm were classified as methicillin-resistant S. aureus (MRSA), whereas isolates with inhibition zones ≥22 mm were classified as methicillin-sensitive S. aureus (MSSA). Phenotypic testing is the standard used in routine public health surveillance and screening programmes.
The questionnaire included questions on general demographic characteristics, health status, social activities, personal hygiene practices, work habits, and home hygiene. The sections concerning general demographic characteristics and health status were completed with the assistance of a physician, whereas the sections related to social activities, hygiene practices, work habits, and home hygiene were self-completed by the participants at their workplaces.
Statistical analyses were performed using SPSS version 16.0 (SPSS Inc., Chicago, IL, USA). Associations between nasal carriage of S. aureus and categorical variables were assessed using the chi-squared test. Prevalence estimates were calculated with 95 % confidence intervals (CI). A p-value <0.05 was considered statistically significant.
Among the 289 food handlers, 36 (12.5 %, 95 % CI: 8.7–16.3 %) were nasal carriers of S. aureus; 34 (11.8 %, 95 % CI: 8.1–15.5 %) of MSSA, and two (0.7 %, 95 % CI: 0–1.7 %) of MRSA (Table 1).
Prevalence of MSSA and MRSA nasal carriage among food handlers in Skopje (with 95 % CI)
| Category | N | Prevalence (%) | 95 % CI |
|---|---|---|---|
| MSSA and MRSA | 36 | 12.5 | 8.7–16.3 |
| MSSA | 34 | 11.8 | 8.1–15.5 |
| MRSA | 2 | 0.7 | 0–1.7 |
MRSA – methicillin-resistant S. aureus; MSSA – methicillin-sensitive S. aureus
We found no statistically significant associations between S. aureus nasal carriage and any of the investigated parameters, including gender, job, body mass index, tooth brushing frequency, facial hair presence, nail hygiene, nose picking, nose rinsing, and hand washing (Table 2).
Nasal S. aureus carriage association with gender, job, body mass index, tooth brushing frequency, facial hair presence, nail hygiene, nose picking, nose rinsing, and hand washing
| Variable | Nasal carriers | Non-carriers | Total | Chi-square | df | p | ||
|---|---|---|---|---|---|---|---|---|
| n | % | n | % | n | ||||
| Gender | ||||||||
| Male | 22 | 15.7 | 118 | 46.6 | 140 | 2.642 | 1 | 0.104 |
| Female | 14 | 9.4 | 135 | 53.4 | 149 | |||
| Total | 36 | 12.5 | 253 | 100 | 289 | |||
| Job | ||||||||
| Cook, baker, assistant cook | 2 | 28.6 | 5 | 71.4 | 7 | 5.676 | 9 | 0.772 |
| Distributor | 1 | 16.7 | 5 | 83.3 | 16 | |||
| Quality control | 0 | 0 | 19 | 100 | 19 | |||
| Storekeeper | 9 | 15.3 | 50 | 84.7 | 59 | |||
| Packager | 1 | 11.1 | 8 | 88.9 | 9 | |||
| Salesman | 0 | 0 | 1 | 100 | 1 | |||
| Worker in production | 19 | 13.1 | 126 | 86.9 | 145 | |||
| Caterer | 2 | 10 | 18 | 90 | 20 | |||
| Cleaner | 1 | 12.5 | 7 | 87.5 | 8 | |||
| Worker | 1 | 6.7 | 14 | 93.3 | 15 | |||
| Body mass index | ||||||||
| Underweight | 1 | 25 | 3 | 75 | 4 | 8.736 | 5 | 0.120 |
| Normal weight | 9 | 8.3 | 99 | 91.7 | 108 | |||
| Overweight | 12 | 10.5 | 102 | 89.5 | 114 | |||
| Obesity class I | 10 | 21.7 | 36 | 78.3 | 46 | |||
| Obesity class II | 4 | 25 | 12 | 75 | 16 | |||
| Obesity class III | 0 | 0 | 1 | 100 | 1 | |||
| Daily tooth brushing frequency | ||||||||
| 0 | 8 | 17.8 | 37 | 82.2 | 45 | 6.546 | 4 | 0.162 |
| 1 | 12 | 16.7 | 60 | 83.3 | 72 | |||
| 2 | 11 | 8 | 126 | 92 | 137 | |||
| 3 | 3 | 10 | 25 | 89.3 | 28 | |||
| ≥4 | 2 | 28.6 | 5 | 71.4 | 7 | |||
| Facial hair | ||||||||
| Beard | 4 | 9.5 | 38 | 90.5 | 42 | 0.388 | 1 | 0.534 |
| No beard | 32 | 13 | 215 | 87 | 247 | |||
| Moustache | 4 | 11.1 | 32 | 88.9 | 36 | 0.068 | 1 | 0.794 |
| No moustache | 32 | 12.6 | 221 | 87.4 | 253 | |||
| Nail hygiene | ||||||||
| Tidy | 28 | 11.6 | 214 | 88.4 | 242 | 1.294 | 1 | 0.255 |
| Untidy | 8 | 17 | 39 | 83 | 47 | |||
| Nose picking frequency | ||||||||
| Often | 3 | 17.6 | 14 | 82.4 | 17 | 2.250 | 3 | 0.522 |
| Rarely | 9 | 17.6 | 42 | 82.4 | 51 | |||
| Very rarely | 9 | 10.2 | 79 | 89.8 | 88 | |||
| Not at all | 15 | 11.3 | 118 | 88.7 | 133 | |||
| Nasal rinsing before work | ||||||||
| Yes | 13 | 12.5 | 91 | 87.5 | 104 | 2.061 | 2 | 0.357 |
| No | 19 | 14.7 | 110 | 85.3 | 129 | |||
| Sometimes | 4 | 7.1 | 52 | 92.9 | 56 | |||
| Nasal rinsing after work | ||||||||
| Yes | 11 | 12.8 | 75 | 87.2 | 86 | 0.194 | 2 | 0.907 |
| No | 19 | 12.9 | 128 | 87.1 | 147 | |||
| Sometimes | 6 | 10.7 | 50 | 89.3 | 56 | |||
| Hand washing after using restroom | ||||||||
| Yes | 34 | 12 | 249 | 88 | 283 | 2.449 | 1 | 0.118 |
| Sometimes | 2 | 33.3 | 4 | 66.7 | 6 | |||
| Hand washing with soap after nose picking | ||||||||
| Yes | 26 | 12.6 | 180 | 87.4 | 206 | 1.325 | 2 | 0.515 |
| No | 5 | 9.1 | 50 | 90.9 | 55 | |||
| Sometimes | 5 | 17.9 | 23 | 82.1 | 28 | |||
However, higher nasal carriage prevalence was observed among men, cooks, bakers, and assistant cooks, participants with untidy nails, those who reported never picking their nose, those not rinsing their nose before or after work, and those who only sometimes washed their hands after using the toilet or after nose picking.
Overall, nasal S. aureus carriage was consistently present among food handlers, with slight variations across gender, job category, body mass index, and hygiene habits, but the differences were not statistically significant. The overall prevalence of 12.5 % falls within the range reported across countries and occupational groups. Two studies from Turkey (14, 15) reported MSSA prevalence rates of 3.37 % and 15.25 % and MRSA rates of 5.3 % and 2.6 %, respectively. In Portugal (12), MSSA prevalence rate was 19.8 %, while in Greece (16) MSSA and MRSA rates were 13.8 % and 0.6 %, respectively. Studies from Ethiopia (17) documented an 11.3 % prevalence of S. aureus. In the United States of America (18), MSSA and MRSA were reported at the rates of 23.3 % and 3.6 %, respectively, and in Hong Kong (19), the overall prevalence of S. aureus was reported at 22.9 %.
Although Beyene et al. (17) reported a significant association between cooks and S. aureus carriage (p=0.00336), our results are not in line with this finding and suggest that occupational exposure may not be the sole determinant of nasal colonisation in this setting.
Regarding gender, our study found no statistically significant difference between men and women, which is consistent with the findings reported by Beyene et al. (17). However, a slightly higher prevalence was observed among men, in line with previous population-based studies reporting male sex as a risk factor for nasal S. aureus carriage (20).
Furthermore, our findings do not support reports of obesity as a risk factor for S. aureus nasal carriage, potentially due to impaired immune function, altered microbiome, and chronic inflammation (21).
Research on the specific contribution of facial hair among food handlers is limited, but facial hair management may influence bacterial colonisation. Our findings are consistent with Wakeam et al. (22), who found no association between facial hair and nasal carriage of S. aureus among health workers. Similarly, a Turkish study reported no significant differences in carriage between men with or without a moustache (23).
According to good hygiene practice standards, food handlers have to maintain good hand hygiene (24), which is critical in reducing the risk of S. aureus colonisation and transmission, hand washing in particular (25). While our study found no significant association between hand washing and nasal carriage, higher carriage rates were observed among participants who only sometimes washed their hands after nose picking. In addition, nail condition also showed no significant association, although participants with untidy nails had slightly higher carriage rates.
Nose picking has been reported as a risk factor for nasal carriage, with Wertheim et al. (26) reporting higher colonisation among frequent pickers. Although no statistically significant association was observed in our study, the highest carriage rate was identified among participants who reported picking their nose often and rarely.
Oral hygiene may also play a role in nasal S. aureus colonisation, as the oral cavity is a common bacterial reservoir (27, 28). However, toothbrushing frequency was not significantly associated with nasal carriage in our sample.
Nasal rinsing, particularly with water or saline solutions, has been shown to reduce S. aureus carriage by physically removing bacteria, disrupting biofilms, and inhibiting bacterial growth (29, 30). Although not statistically significant in our study, slightly lower carriage rates were observed among participants who reported rinsing their noses.
Our study has several limitations. First, the presence of S. aureus in the nasal cavity does not necessarily indicate enterotoxin production, and we did not determine classical enterotoxin genes (sea, seb, sec, sed, see). Second, laboratory analyses relied on culture-based and phenotypic methods for identifying MSSA and MRSA, while molecular confirmation of resistance mechanisms (e.g. mecA PCR) was not performed, as this is not the scope of routine health and hygiene surveillance programs. Although PCR detection of the mecA gene is considered the molecular gold standard, phenotypic detection using the cefoxitin disc diffusion method has shown high agreement with PCR results and remains a reliable and widely accepted method for routine MRSA screening (31). Third, self-reporting necessarily entails the risk of bias. Fourth, the study was conducted in Skopje over five months and may not capture seasonal variations or reflect all regions of the country. Data on specific work practices which may influence nasal colonisation risk, including contact with raw products or shift duration, were not detailed in the questionnaire. Finally, our study focused on nasal carriage without linking it to clinical outcomes or food contamination events. These considerations provide context for interpreting the findings and may guide future research in the field.
Our study showed a 12.5 % nasal carriage prevalence of S. aureus among food handlers and no significant associations with gender, BMI, facial hair, nail condition, or specific hygiene practices, although slightly higher carriage rates were observed among men, cooks, and individuals with untidy nails. However, our findings should be interpreted with caution, and future studies should address the limitations of the present study. Targeted training, routine screening, and consistent adherence to good hygiene practices remain important for minimising colonisation and reducing the risk of S. aureus transmission.