A swine origin influenza A virus epidemic was initiated in April 2009 with the first cases appearing in Mexico and the United States. The virus acquired rapid transmissibility and pandemic potential with more than 340,000 laboratory-confirmed cases and more than 4100 deaths reported to the World Health Organization (WHO) as at September 27, 2009. Given the evidence of sustained community-level outbreaks of novel Influenza A(H1N1) in more than one WHO region, WHO designed the virus as “pandemic influenza A(H1N1) 2009 virus” [1] .

The outbreak was first observed in Mexico, with evidence that there had been an ongoing epidemic for months before it was officially recognized [2] . The Mexican government soon closed most of Mexico City’s public and private offices and facilities to contain the spread of the virus. As the virus quickly spread globally, clinics were overwhelmed by testing and treating patients, and the WHO and the US Centers for Disease Control and Pre- vention (CDC) eventually stopped counting all cases and focused instead on tracking major outbreaks. On June 11, 2009, the WHO declared the outbreak to be a pandemic [3] .

Only mild symptoms are experienced by the overwhelming majority of victims, but there are exceptions. Some persons are in higher risk groups, such as those with heart disease, asthma, obesity, diabetes, children with neurodevelopmental conditions [4] [5] , or pregnant women, and immune compromised individuals [6] . However, a small subset of previously healthy young adults rapidly developed severe pneumonia, typically 3 to 5 days af- ter the initial onset of symptoms with rapid deterioration progressing to respiratory failure within 24 hours, re- quiring intensive care and ventilation support [7] . Like other influenza viruses, swine flu is typically contracted by inhaling air that has been contaminated by an infected person coughing or sneezing, or by touching one’s nose or mouth with hands that have previously touched contaminated surfaces and have not been disinfected. Symptoms, which last up to a week, are similar to those of seasonal flu, and can include fever, sneezing, sore throat, cough, headache, and muscle or joint pains. To avoid spreading the infection, the CDC recommended that those with symptoms stay home from school, work, and crowded settings. Wearing facial masks was not rec- ommended except in health care settings [8] . On the other hand, the swine flu outbreak has led to numerous precautionary school closures in several countries. Rather than closing schools, in August 2009 the CDC rec- ommended that students and school workers with flu symptoms should stay home for either seven days total, or until 24 hours after symptoms subside; whichever is longer [9] . The CDC also recommended that colleges should consider suspending fall 2009 classes if the virus began to cause severe illness in a significantly larger share of students than the previous spring. Different countries adopted strategies to control the spread of the novel in- fluenza A(H1N1) virus, especially among the schools, by promoting hand hygiene, vaccination priority, and school closures if required [10] - [16] .

The city of Makkah is situated to the west of The Kingdom of Saudi Arabia (KSA), and has an influx of people from multiple nationalities, since it is the holy pilgrimage site for Muslims all over the world. Tradition- ally, the KSA, its leadership, health authorities, and all people have committed to serving the pilgrims of the Holy places in Makkah and Medinah ensuring that guests can perform their rituals with ease and dignity. It is es- timated that between 2 and 3 million pilgrims from all over the world perform Hajj annually, which, being the largest gathering of people, facilitates the spread of various infectious agents including viruses [17] . This study was conducted to describe the epidemiology of influenza A(H1N1) infections in KSA among residents, citizens, and students in Makkah city during 2009.

A total of 1138 subjects were studied during the study period. The majority (81%) of the persons suspected to have influenza A(H1N1) among the study population were between 5 and 45 years old. Among these, the maxi- mum percentage (24.8%) of persons were between 15 and 24 years old, while 20% were between 10 and 14 years old, and 14% were between 25 and 34 years old. Among the citizens and residents, most of the suspected cases were between 15 and 44 years old (60.4%), while among the students, most of the cases were between 5 and 24 years old (91.8%) representing preparatory, primary and secondary stages. Around 6% of the suspected cases for Influenza A(H1N1) in schools were the employees. The details are given in (Table 1).

The results of the PCR test showed that, the citizens and residents had the maximum percentage of PCR-pos- itive cases in the 15 - 34 years age group (49.3%) among other categories. In the student group, the highest per- centage of PCR-positive cases was between 5 and 24 years (93.3%). The cumulative PCR positivity among the study subjects was the highest among the 15 - 24 years age groups (24.6%). Nearly half of the PCR-positive cases for Influenza A(H1N1) students (48%) were in the primary school age group (10 - 14 years) and 26% (5 - 9 years) age group; while students in the secondary school age groups represented (19%) of PCR-positive for Influenza A(H1N1), which was the lowest percentage among other school stages. Employees in schools ac- counted for 8% of PCR-positive cases for Influenza A(H1N1). The cases were compiled by age distribution through grouping the cases at 5-year intervals. Table 2 shows the details of distribution. Figure 1 illustrates the percentage of total distribution among the age groups.

The sex distribution shows that among the residents and citizens, males accounted for 55% of the cases while 45% were females with a male-to-female ratio of 1:1.22. Similarly, in the student groups, the male-to-female ra- tio was 1:1.1. The details are given in (Table 3). The analysis of PCR results by gender revealed that overall, around 58% of the males were positive while around 42% were females (Table 4). More than one-half (55%) of the persons suspected for Influenza A(H1N1) among the population were males and the rest were females (45%). This ratio was about the same for students where males were 52% and the rest were females (48%). There was

no statistically significant difference in the PCR positivity based on the gender distribution among both the citi- zen and student groups (P = 0.886).

Out of the total study population, 74.9% were citizens, while the remaining 20.5% were visitors from different nationalities (Table 5). Among the student subgroups, 85.7% were citizens, and 14.3% were non-citizens. The distribution of the PCR-positive cases for Influenza A(H1N1) among study population showed that; the highest positive cases were among citizen and residents as it shown in Table 6.

The highest percentages of PCR-positive cases for Influenza A(H1N1) were seen at primary school levels with 33.3% frequency for males and 21.8% for females (Table 7). However, at secondary school levels for males and females, these frequencies dropped to 7.0% and 6.8%, respectively. Intermediate frequency percen- tages of 17.8% (males) and 12.3% (females) were observed at preparatory education levels.

PCR-positive cases for Influenza A(H1N1) primarily among male students presented more than half (52.6%) of all cases (Figure 2), whereas the percentage among female students was 47.4%. Among male students, Pa- kistani boys showed the highest percentage (Figure 3), while Egyptian girls showed the highest percentage among female students (Figure 4).

Annual influenza epidemics are estimated to affect 5% - 15% of the global population. Although most cases are mild, these epidemics still cause severe illness in 3 - 5 million people and 250,000 - 500,000 deaths worldwide [19] . On average, 41,400 people die each year in the United States based on data collected between 1979 and 2001 [20] . In industrialized countries, severe illness and death occurs mainly in the high-risk populations of in- fants, the elderly, and the chronically ill [18] , although the swine flu outbreak (as well as the 1918 Spanish flu) differs in its tendency to affect younger, healthier people [20] .

Influenza is an annual major public health threat. Each year, the influenza vaccine is targeted against the strains (usually from the past year) that are expected to circulate in the next season. However, when a major an- tigenic shift occurs, time is insufficient to manufacture a vaccine for the first wave of the ensuing pandemic [21] [22] . Since 1977, A(H1N1) strains have been isolated in the United States with varying frequency [23] - [25] . The majority of A(H1N1) isolates in 1984 and 1985 resembled the A/Chile/1/83 strain, and subsequently this antigen was included in the trivalent influenza vaccines for the 1984-1985, 1985-1986, and 1986-1987 influenza seasons [24] - [26] . Swine influenza (also called swine flu, hog flu, pig flu, and sometimes, the swine) is an infection by any one of several types of swine influenza virus (SIV). It is any strain of the influenza family of viruses that is endemic in pigs. As at 2009, the known SIV strains included influenza C and the subtypes of Influenza A known as H1N1, H1N2, H3N1, H3N2, and H2N3 [21] .

These strains of swine flu rarely pass from human to human. Symptoms of zoonotic swine flu in humans are similar to those of influenza and of influenza-like illness in general, namely chills, fever, sore throat, muscle pains, severe headache, coughing, weakness, and general discomfort with gastrointestinal symptoms such as vomiting and diarrhea [21] [25] [27] .

The results showed that 81% of the studied population was between 5 and 45 years of age. In the student sub- group, 69% of subjects belonged in the 10 - 24 years age group. In the study population, 27% of Influenza A(H1N1)-positive cases were between 15 and 24 years old, while in the student subgroup, 48% of PCR-positive

cases were seen in the primary school stage. The highest percentage (25%) of PCR-positive cases in citizens/ residents (27%) and students (19%) were seen in those between 15 and 24 years of age. Similarly, in a smaller cohort of population studied by Al-Mazroa et al. [28] , the highest percentage of the cases were in the age group of 20 - 30 years old followed by the age group of 1 - 10 years old. However, an important factor for the in- creased incidence of A(H1N1) cases among the younger population groups may be attributable to increased ac- tivity and movement. All positive cases received treatment and recovered completely. In Makkah, school clo- sures were not undertaken based on the criteria of 10% of cases among students and employees or 10% absen- teeism. We had a strong and effective health education program aimed at the whole community and specifically towards students. Responsibility can also be credited to the good coordination between the departments of health affairs and education.

No school closures were undertaken during the study period. Effective measures taken by Saudi health au- thorities at all levels played a key role in prevention and control of A(H1N1) among the residents and students. Previous studies on Hajj pilgrims suggested a high incidence of influenza-related respiratory tract infections with approximately 24,000 cases seen every year [17] . Furthermore, the seasonal influenza vaccination rate among visiting pilgrims was quite low. In order to prevent an emergence of novel influenza viruses during the Hajj event and the year-round Umrah gathering in Makkaha, steps like non-pharmaceutical interventions, en- hanced surveillance with screening, ensuring quarantine at the entry points, mandatory vaccination for seasonal flu, and timely provision of diagnostic facilities may be implemented. Health education and public awareness regarding safety precautions including vaccinations may be the best long-term efforts towards effective control of H1N1 influenza.

Further analysis of the information obtained from this study will be important to understand their diversity and evolutionary history in comparison with the swine Influenza A(H1N1) worldwide [29] [30] .

A total of 1138 subjects, irrespective of age and sex, were included in the study. Among the study population, 25% of the cases in the age group between 15 and 24 years old were found positive for Influenza A(H1N1) by the PCR technique. Although a significant population was affected by Influenza A(H1N1) during 2009 in Makkah, the efforts and steps taken by health authorities at all levels, especially those in Directorate of Health Affairs of Makkah helped to avert the mortality associated with Influenza A(H1N1) among the residents and those coming for Umra and Hajj to Makkah by providing treatment facilities and timely diagnosis. Because the influenza vi- ruses mutate and produce new strains, we stress the importance of following basic instructions and dissemina- tion the information among the community, which will limit the spread of the disease. This includes the yearly flu vaccination as the first and most important step in protecting against Influenza. Covering the nose and mouth with a tissue when coughing or sneezing, throwing the tissue in the trash after using, and washing the hands of- ten with soap and water is also recommended. If soap and water are not available, the use of an alcohol-based hand rub can be an alternative method, as well as avoiding touching the eyes, nose, and mouth as germs can be spread that way. If someone is getting sick, they should stay home from work or school and limit contact with others to keep from infecting them. Public health advice must be followed regarding school closures, avoiding crowds, and other social distancing measures to reduce or prevent the spread of Influenza.

The author greatly thanks Mr. Adel Al-Zahrani for PCR sample preparation and Dr. Kamal QamarAlanbia for his suggestions.

There was no financial or other form of conflicts of interest to any of the authors.