Haemophilus influenzae


Haemophilus influenzae (H. influenzae) are bacteria commonly carried in the respiratory tract, which can cause acute invasive disease. They are divided into encapsulated and unencapsulated (non-typeable) strains. Encapsulated strains can be classified into six serotypes, from a to f, of which type b (Hib) was most prevalent prior to vaccine introduction. Infection with H. influenzae can cause the following conditions:

  • meningitis
  • septicaemia
  • acute respiratory infections

Less frequent conditions which may be caused by H. influenzae infection include:

  • epiglottitis
  • osteomyelitis
  • septic arthritis

For more information on H. influenzae, visit the NHS Inform website.


Guidance on Haemophilus influenzae can be found below:

For all infection prevention and control guidance visit the A-Z ​pathogens section of the National Infection and Prevention Control Manual.

Data and surveillance

In 1992, following introduction of the Hib vaccine for young children, the number of H. influenzae type b cases fell dramatically, not only in the vaccinated group but also in older age groups.  Due to reduced carriage of the organism within the respiratory tract of vaccinated children, transmission to the wider community was effectively suppressed. The addition of the Hib booster vaccine in 2006, reduced case numbers further.

In Scotland, typing is conducted on  all cases with positive laboratory reports for H. influenzae, in order that national trends in disease subtypes can be monitored. Further enhanced surveillance is carried out for all H. influenzae cases identified in children under the age of 5 and type b strains across all age groups.

Surveillance update for October to December 2020

Nine cases of invasive H.influenzae were reported in the last quarter of 2020, bringing the total for 2020 to 49. This is lower than the cumulative case numbers reported for the previous four years (range 78 to 99), as shown in Figure 1.

Figure 1: Cumulative number of Haemophilus influenzae cases reported to HPS, 2016 to 2020 (week 52)  

Line graph showing a steady increase in cumulative number of cases per week in all years.

Of the 49 cases reported in 2020:

  • three (6.1%) were aged under five years
  • three (6.1%) were aged between five and twenty years
  • six (12.2%) were aged between 21 and 40 years
  • 37 (75.5%) were aged over 40 years of age

Of the 49 cases reported in 2020:

  • 42 (85.7%) had influenzae isolated from blood
  • five (10.2%) from pleural fluid
  • two (4.1%) from cerebrospinal fluid

There were no known deaths associated with H.influenzae in 2020.

Figure 2 demonstrates the epidemiological impact of the Hib vaccine, for those aged under five (routinely vaccinated group) and for all ages (including under fives). There was a marked decrease in cases from 1992 in all age groups, followed by a rise in case numbers in the early 2000s. Case numbers decreased again following the introduction of the Hib booster vaccine, and figures have remained relatively stable since 2011.

Figure 2: Laboratory reports of invasive Haemophilus influenzae type b disease in Scotland, 1988 to 2020 (week 52)

Line graph showing a sharp decrease in cases of invasive H. influenza in all age groups following the introduction of the vaccine in 1992 and booster in 2003.

Figure 3 presents laboratory reports by serotype, since the introduction of the Hib booster campaign in 2003.

H. influenzae typing was carried out for 36 (73.5%) isolates, of which:

  • 30 (83.3%) were non-typeable (NT)
  • four (11.1%) were type f
  • one (2.8%) was type a
  • one (2.8%) was type b 

Figure 3: Laboratory reports of Haemophilus influenzae by serotype, 2003 to 2020 (week 52)

Chart showing a steady decline in type b infection since introduction of the Hib vaccine in 2003, with a corresponding increase in non-typeable strains.


Vaccine uptake statistics

Vaccine uptake statistics are published by Public Health Scotland Data and Intelligence.